Concave Cavity Research Articles

Enantiospecific recognition of 2-butanol by an inherently chiral cavitand in the solid state

A new inherently chiral cavitand is described, in which the desymmetrization of the rigid concave cavity is achieved by introducing three different bridging groups at the upper rim, namely two inward PO groups, one inward PS moiety and one methylene bridge in the AABC mode. The racemic mixture of cR and cS enantiomers is resolved by semi-preparative chiral HPLC and the enantiopurity confirmed through circular dichroism. The properties of the enantiopure cR-cav in the enantioselective recognition of racemic 2-butanol is studied by co-crystallization experiments. The exclusive formation of the complex R-BuOH@cR-cav demonstrates that cR-cav is able to discriminate between the two enantiomers of the alcohol in the solid state. The enantiospecific recognition exhibited by the cR-cav towards racemic 2-butanol is particularly relevant because of the low degree of chirality of the alcohol (1.9 calculated by CCM algorithm).

Process window calculation and pressure locus optimization in hydroforming of conical box with double concave cavities

With the enhancement in the functional integration of components and concentration on lightweight materials, complex sheet metal parts are widely used in automobile and aviation industrial clusters. Consequently, the sheet hydroforming process has become an attractive fabricating technology for forming lightweight materials and complicated products. In this research, the hydrodynamic deep drawing (HDD) process of a composite conical box with double concave cavities was investigated through theoretical analysis, numerical simulation, and process experimentation. Furthermore, the process window diagram (PWD) was calculated using the stress analytical model combining material properties with workpiece geometrical features. The influence of cavity pressure loading locus on the forming quality of the fabricated part and the deformation behavior of aluminum alloy was explored. The forming results indicated that the initial pressure, full pressure, and loading locus are the fundamental parameters directly related to the forming quality and dimensional accuracy. For the conical part with composite features, the reasonable initial pressure value is crucial for the thickness homogeneity of the double concave characteristics, whereas the magnitude of the full pressure is vital for improving the quality of the conical feature. In addition, the optimal loading locus of the cavity pressure is characterized by two turning points, which are related to the punch corner radius, die shoulder radius, blank thickness, and angle of the conical feature.

Flow characterization and mixing performance of weakly-shear-thinning fluid flows in a microfluidic oscillator

In this study, the characteristics and mixing performance of weakly-shear-thinning fluid flows through a microfluidic oscillator are investigated. The effects of three different geometric parameters are investigated: the radius of the concave curvature, the feature of the conjunct channel, and the edge shape of the cavity. Using Carbopol 934 aqueous solution as the working fluid, we quantify the mixing performance with fluorescence imaging, identify the flow patterns from particle tracking technique, and determine the frequency of flow oscillation from the pressure signal at different flow rate. For the microfluidic oscillator, rounding the corner of the bluff body extends the arc length of the concave cavity and thus increases the Görtler vortex instability, resulting in an enhancement of mixing. For Carbopol 934 solution, this effect actually dominates over the influence of the conjunct geometry, albeit that a concave cavity with smaller radius of curvature is usually preferred. Comparing to the Newtonian fluid flows, passing the weakly-shear-thinning fluid though a microfluidic oscillator leads to a slower oscillation with smaller amplitude. This diminishes the impact of flow instability on the mixing performance, and mass transport of the weakly-shear-thinning fluid replies more heavily on the advection effect. Due to the weakly-shear-thinning characteristics, flow patterns of the Carbopol 934 solution fluid in microfluidic oscillators are subtly different. However, the spectrum analysis reveal that the oscillation frequency increases linearly with the inlet velocity and flow metering remains possible when weakly-shear-thinning fluid is applied. Herein, we establish the functional relationship between the flow rate and the frequency for the Carbopol 934 solution so that the detected frequency can be employed to accurately estimate the flow rate.

Assembly of porous smectic structures formed from interlocking high-symmetry planar nanorings

Materials comprising porous structures, often in the form of interconnected concave cavities, are typically assembled from convex molecular building blocks. The use of nanoparticles with a characteristic nonconvex shape provides a promising strategy to create new porous materials, an approach that has been recently used with cagelike molecules to form remarkable liquids with "scrabbled" porous cavities. Nonconvex mesogenic building blocks can be engineered to form unique self-assembled open structures with tunable porosity and long-range order that is intermediate between that of isotropic liquids and of crystalline solids. Here we propose the design of highly open liquid-crystalline structures from rigid nanorings with ellipsoidal and polygonal geometry. By exploiting the entropic ordering characteristics of athermal colloidal particles, we demonstrate that high-symmetry nonconvex rings with large internal cavities interlock within a 2D layered structure leading to the formation of distinctive liquid-crystalline smectic phases. We show that these smectic phases possess uniquely high free volumes of up to ∼95%, a value significantly larger than the 50% that is typically achievable with smectic phases formed by more conventional convex rod- or disklike mesogenic particles.

PMMA Micro-Pillar Forming in Micro Channel by Hot Embossing

Abstract Micro-pillars forming in micro channels have been implemented by hot embossing. With dry etching and chrome photo mask, the silicon mold was fabricated using lithography process for manufacturing micro-pillars in micro channels. The hot embossing experiments are executed on the embossing machine by embossing the PMMA substrate and the silicon mold. Making the polymer filling in the concave cavity of the silicon mold is a difficulty, so the laws of polymer filling in the concave cavity were researched. The effects of three key embossing parameters including pressure, temperature and time on the PMMA replication accuracy were studied, and the optimal molding parameters were obtained. This work is instructive to fabricate microfluidic chips with micro-pillars.

Dynamics of Hydration Water around Native and Misfolded α-Lactalbumin.

As water is an essential ingredient in protein structure, dynamics, and functioning, knowledge of its behavior near proteins is crucial. We investigate water dynamics around bovine α-lactalbumin by combining molecular dynamics simulations with polarization-resolved femtosecond infrared (fs-IR) spectroscopy. We identify slowly reorienting surface waters and establish their hydrogen-bond lifetime and reorientation dynamics, which we compare to the experimentally measured anisotropy decay. The calculated number of slow surface waters is in reasonable agreement with the results of fs-IR experiments. While surface waters form fewer hydrogen bonds than the bulk, within the hydration layer water is slower when donating more hydrogen bonds. At concave sites the protein-water hydrogen bonds break preferably via translational diffusion rather than via a hydrogen-bond jump mechanism. Water molecules reorient slower near these sites than at convex water-exposed sites. Protein misfolding leads to an increased exposure of hydrophobic groups, inducing relatively faster surface water dynamics. Nevertheless, the larger exposed surface slows down a larger amount of water. While for native proteins hydrating water is slower near hydrophobic than near hydrophilic residues, mainly due to stronger confinement, misfolding causes hydrophobic water to reorient relatively faster because exposure of hydrophobic groups destroys concave protein cavities with a large excluded volume.

Supramolecular trap for a transient corannulene trianion.

The first structural characterization of the transient triply-reduced state of corannulene (C20H10) is accomplished. The X-ray crystallographic study reveals that the C20H10˙3- trianions, generated by corannulene reduction with metallic cesium, form a novel type of supramolecular sandwich-type assembly, [Cs+//(C20H103-)/4Cs+/(C20H103-)//Cs+]. In the product, two triply-charged corannulene decks encapsulate a rectangle of four cesium ions with the external concave bowl cavities being filled by one cesium ion each. The structural investigation is augmented by in-depth theoretical calculations to provide insights into the geometrical features and electronic structure of this unique organometallic self-assembly.

Convective heat transfer by a row of tab-excited impinging jets on a wedge-shaped concave surface

A Computational study was conducted to investigate the convective heat transfer characteristics by a row of tab-excited air jets impingement on a wedge-shaped concave surface having larger curvature than semi-circular concave surface. The geometric effects, including the tab number and tab penetration ratio, as well as the offset-jets arrangement, on the impinging jet flow and heat transfer behaviors are analyzed under several non-dimensional jet-to-leading edge distances (6, 9, 12) and the jet Reynolds numbers ranging from 6900 to 26,100. The results show that both the jet offset-arrangement and tab-excitation are proved to be capable of improving the convective heat transfer in the vicinity of jet impingement region. Either for the conventional round jet or tab-excited jet, it appears that an optimum non-dimensional jet-offset distance is about 1.5. The heat transfer enhancement is improved as the increase of tab number (ranging from 4 to 8), as well as tab penetration ratio (ranging from 0.13 to 0.25). The influence intensity of non-dimensional jet-offset distance on the convective heat transfer inside a concave cavity is more significant for the tab-excited jet impingement than that for the conventional round jet impingement. In general, the effects of jet offset-arrangement and tab-excitation on the jet impingement heat transfer enhancement behave more significant under larger jet Reynolds number as well as smaller impingement distance.

Growth mechanism of icosahedral and other five-fold symmetric diamond crystals

Five-fold symmetric diamond crystals (FSDCs) were synthesized by hot filament chemical vapour deposition (HFCVD) methods. Their surface morphologies and defects were characterised by scanning electron microscopy (SEM). From the perspective of nucleation-growth, a growth mechanism for icosahedral and other five-fold symmetric diamond crystals was discussed. Computer modelling was also carried out. The results show that the dodecahedrane (C20H20) molecule is proposed as a nucleus for the growth of icosahedral diamond crystals (IDCs), wherein the 20 {111} surface planes develop orthogonal to the direction of the original 20… C…H bonds by sequential H abstraction and CH3 addition reactions. IDC can be pictured as an assembly of isosceles tetrahedra, with each tetrahedron contributing a {111} plane to the surface of the IDC and the remainder of the tetrahedral surfaces forming twin planes with neighbouring tetrahedra. The small mismatch (1.44°) between the {111} surface dihedral angle of a perfect icosahedron and that of a twinned icosahedron reveals itself via twin planes in the IDC grain. The modelling suggests how the relief of strain induced by this distortion could lead to the formation of defects such as concave pentagonal cavities at vertices and grooves along the grain edges that accord well with those observed experimentally. Similar arguments based on growth from the hexacyclo pentadecane (C15H20) nucleus can also account for the observed formation of star and rod shaped FSDCs, and some of their more obvious morphological defects.

Numerical investigations on characteristics of methane catalytic combustion in micro-channels with a concave or convex wall cavity

Catalytic combustion characteristics of methane in micro-channels with a concave and convex cavity, respectively, and in straight channel without cavity were numerically investigated. The results show that as the equivalence ratio (ϕ) increases, the methane conversion increases first and then decreases, the highest methane conversion ratio, which is 85.3%, occurs at ϕ=1.0 in the micro-channel with convex wall cavity. The micro-channel with concave wall cavity is not conductive to methane catalytic micro-combustion at relatively low velocity. With the inlet velocity increasing, the methane conversion ratio is decreased. In the micro-channel with convex wall cavity, the inner wall pressure increases, because the fuel is disrupted when it flows through the cavity. Then the mixture of methane contact with catalyst is enhanced, which favors the combustion of methane. The recirculation zone which is the largest area formed in the micro-channel with convex wall cavity absorbs more high temperature gas and raises the combustion temperature. Heat transfer in the convex micro-channel is enhanced which makes the temperature distribution more uniform. The maximum value of the extinction limit is 16.5m/s, which occurs in the micro-channel with convex cavity.

MICROLEAKAGE ASSOCIATED WITH RETROGRADE FILLING AFTER ROOT END RESECTION (in vitro study)

SUMMARY: The purpose of the study is to compare microleakage after root end resection of the two materials (MTA and Biodentine) for two different apical cavity preparation using the method of penetration of dye - 0, 2 % Rodamine B. Materials and Methods: Forty-eight extracted single-rooted human teeth were used in this study. The resection was made at 3 mm from the root tip with a high speed diamond bur at an angle of 90 degree to the long axis of the tooth. For the retrofilling, ProRoot MTA and Biodentine were used. The teeth were divided into 5 groups: 1 st group (10 teeth) – the apical cavity was prepared with stainless steel fissure bur #10 at 3 mm depth in the root canal parallel to the long axis of the tooth and is filled retrograde with MTA. 3 rd group (10 teeth) - retrofilling with Biodentine. 2 nd group (10 teeth) with a round bur apical cavity was prepared with a concave shape and cavity along the root canal with a depth of 3 mm and retrograde obturation with MTA. 4 th group (10 teeth) retrofilling with Biodentine. 5 th group (8 teeth) - control group - with preparation of the cavity after resection without retrofilling. The outer surface of the root is covered with two layers of varnish, with the exception of the apical 3 mm then immersed in 0.2% Rodamine B for 72 h. The degree of penetration of the dye is measured in millimeters. Results: Relative highest median value of penetration of the dye in mm is in the control group. MTA group has a higher value in mm versus the Biodentine. The apical preparation with a concave shape and cavity along the root canal with a depth of 3 mm after apicoectomy is important to reduce apical microleakage. Conclusion: Different apical cavity preparations in both types of material have led to the microleakage dye, but to varying degrees.

Self-assembly of charged corannulene with cesium ions: Always in the bowl

Cesium salts of mono- and doubly-reduced bowl-shaped corannulene have been prepared in the presence of different O-donors and isolated as bulk crystalline solids. Crystallization of corannulene monoanions with cesium ions from diglyme afforded green blocks of [Cs(diglyme)+(C20H10−)] (1). Its X-ray structural investigation revealed the formation of a 1D polymer built on simultaneous binding of large cesium ion to the convex and concave faces of the adjacent C20H10•− anions, with each bowl functioning in the rare η5-endo:η6-exo bridging mode. The coordination environment of the Cs+ ion is completed by a side-bound diglyme molecule. The cesium salt of corannulene dianion, C20H102−, was crystallized in the presence of dicyclohexano-18-crown-6 ether as [Cs2(dc-18-crown-6)1.52+(C20H102−)] (2). This product has a discrete linear tetranuclear structure built by aggregation of two terminal exo-hub-bound {Cs(dc-18-crown-6)(C20H102−)}− anionic moieties with the central {Cs2(dc-18-crown-6)}2+ cationic gluing block. The cesium ions of the latter, sharing one crown ether molecule, occupy the concave cavities of the doubly-charged corannulene bowls. As a result, each bowl functions in the symmetric η5-endo:η5-exo bridging mode which has not been previously seen. The bowl depths of the resulting carbanions in 1 and 2 are 0.915(15) Å and 0.852(13) Å, respectively, vs. that of 0.875(2) Å in neutral corannulene.

A Differential Evolution Stereo Matching Method in Digital Image Correlation

Stereo matching is widely used in three-dimensional (3D) reconstruction, stereo machine vision and digital image correlation. The aim of stereo matching process is to solve the well-known correspondence problem, which tries to match points or features from one image with the same points or features in another image from the same 3D scene. There are two basic ways, correlation-based and feature-based, are used to find the correspondences between two images. The correlation-based way is to determine if one location in one image looks/seems like another in another image, and the feature-based way to find if a subset of features in one image is similar in the another image. In stereo matching, a simple algorithm is to compare small patches between two rectified images by correlation search. For the pair images acquired from two cameras inevitably exists some rotation transformation, the algorithm first runs a preprocessing step to rectify the images with the epipolar rectification to simplify the problem of finding matching points between images. The epipolar rectification is to determine a transformation of each image plane such that pairs of conjugate epipolar lines become collinear and parallel to one of the image axes. It will lead the loss of gray information of images. The effect is dependent on the amount of angle. When the angle is big enough, the correlation search may yield error results because of retrograded correlation effect. In order to solve the problem, the paper presents an improved stereo matching algorithm with differential evolution to solve the correspondence problem. Our method doesn’t need to runs the preprocessing step to rectify the images with the epipolar rectification. It uses a differential evolution algorithm to minimize the correlation function which contains the angle information after acquiring the epipoar geometry constraint of two image pairs. Then it utilizes a flood-fill algorithm to search correspondence sub-region in the area around the epipolar line. The flood-fill algorithm can overcome the problem of the traditional row-column scanning search method, which will encounter boundary barrier where exists concave polygons or cavities. The Experimental results show that the proposed method can be easily implemented in stereo matching without loss of information of image features with large rotation angle transformation. In the paper, we will introduce the stereo matching principle and its algorithms, including the differential evolution algorithm for finding the correspondences with large rotation transformation between stereo image pairs and the flood-fill traversal strategy for matching large area with complex concave polygons or cavities. In the end of the paper, some experimental results will be given to illustrate the method effectiveness. Keywords: digital image correlation, stereo matching algorithm, epipolar geometry, flood fill algorithm, differential evolution, rotation angle

An Electromagnetic Parameters Measuring System Based on a Concave Cylindrical Cavity

In this paper, an electromagnetic parameters measuring system based on a concave cylindrical cavity is presented. The concave cylindrical cavity resonator mode is with separated electric field and magnetic field distribution region, which is not observed in other cavities. It is shown that permittivity and permeability can be tested by placing samples in the strongest electric field region and magnetic field region, respectively. Therefore, by using this measurement system, the electromagnetic parameters of microwave absorbing materials can be accurately characterized.

Tunable shape transformation of freezing liquid water marbles

Liquid water marbles coated with fumed silica nanoparticles exhibit various shape transformations upon freezing which are dependent on the hydrophobicity of the nanoparticles. The shape can be recovered during re-melting. For marbles coated with the most hydrophobic particles, a vertically prolonged morphology with a pointed protrusion on the top is formed on freezing. For marbles coated with less hydrophobic particles, a lateral expanded flying saucer-shaped morphology is formed. The different responses to freezing result from the different heterogeneous nucleation sites owing to the different positions of the particles at the air-water interface. If the particles are more immersed in water, ice embryos tend to form in the concave cavities between the particles. The volume expansion of water caused by freezing and continuous nucleation lead to continuous lateral stretching of the particle network coating the droplet surface and ultimately to the horizontally inflated shape of the marble. If the particles are more exposed to air, nucleation occurs on the convex surface of the particles, similar to that of a bare water droplet on a hydrophobic substrate.

오목 음향 공동의 고정밀도 고유치 해석을 위한 새로운 MNDIF법 정식 개발

A new formulation of the MNDIF method is introduced to extract highly accurate eigenvalues of concave acoustic cavities. Since the MNDIF method, which was introduced by the author, can be applicable for only convex acoustic cavities, a new approach of dividing a concave cavity into two convex domains and formulating an algebraic eigenvalue problem is proposed in the paper. A system matrix equation, which gives eigenvalues, is obtained from boundary conditions for each domain and the condition of continuity in the interface between the two domains. The validity and accuracy of the proposed method are shown through example studies.

Experiment Research of Polishing Capability of Magnetorheological Finishing with a Small Permanent Magnet Ball-End Tool

In order to resolve the difficulty in polishing work of complex shape, a new magnetorheological finishing (MRF) technology with a small permanent magnet ball-end tool is developed. Rotary symmetrical magnetic field generated by the small permanent ball-end tool, stiffen a magnetic fluid which is delivered by a slender needle tubing, in contact with a workpiece. The permanent magnet tool is hold by a slender cylindrical shank, so it won’t interfere with workpiece when polishing deep concave cavity. A prototype apparatus is established to study the processing characteristics of this polishing method. MRF spots are taken on stationary workpiece to study the influence of several processing parameters on the material removal function, such as, spindle speed, included angle and minimum gap between polishing tool and finishing-surface. A 3×3mm square on a fused quartz (FS) is polished and the surface roughness decrease from 81nm Ra to 1.5nm Ra after polishing for 100min.

Study of Turbulence Characteristics in Different Advanced Vortex Combustor Structure

Based on the idea of single cavity trapped vortex combustor, a advanced vortex combustor which is constitute by three blunt bodies and double concave cavity is proposed. And the interior combustor flow characteristics are analyzed. The results shows that the flow field characteristics changed a lot before and after combustor modification, and D2=20mm, D3=4mm are respectively the best modification scheme on the second and third blunt body.

Isotropically Etched Silicon Microarrays for Rapid Breast Cancer Cell Capture

In this paper, we describe design and fabrication of 3-D silicon microarrays consisting of a wide range of isotropically-etched concave cavities for cell-capturing applications. The microarrays supported rapid and efficient capture of metastatic human breast cancer cells (MDA-MB-231) from single-cell suspensions. Furthermore, the captured cells adhered and were retained within the etched cavities for at least 72 h. Cavity spacing of 30-50 μm was most suitable for capture of the cells within microwells. Cell capture was evident within 1 min and was essentially complete by 20-30 min. Capture of 10 μm beads proceeded with a similar time frame and efficiency. Cell capture was 80%-90% efficient and was independent of cavity diameters tested: 35, 60, 70, and 100 μm. The depth of the microwells ranged from 28 to 54 μm. For single-cell capture, the 35 μm diameter cavity was optimal. The larger cavities contained 3-10 cells and were better suited for applications sensing cell proliferation, cell-cell interactions, stem cell differentiation, and drug responsiveness. The proposed silicon microarrays did not require any chemical coating or surface modification to support micro co-cultures of normal human breast epithelial cells (MCF10A) and MDA-MB-231 after cell trapping. This paper demonstrates that the silicon microarrays efficiently capture individual human breast cancer cells from a mono-culture suspension and in a mixture of excess MCF10A. Therefore the developed silicon platform is suitable for efficient detection and sensing of individual human breast cancer cells.

Diode-end-pumped frequency-doubled Nd:YAP/Cr:YAG laser using a KTP crystal

We present a design for a compact laser-diode-end-pumped Nd:YAP/Cr:YAG q-switched laser in a plano–concave cavity configuration. With an optical-to-optical efficiency of 35%, this laser provides an average output of 1.2 W with 13 mJ at 1080 nm. After that, the laser is frequency doubled by replacing the output coupler with a flat KTP crystal to achieve an output of 8 mJ in 8 ns at 540 nm. At a peak power of 1 MW, the laser emits linearly polarized output with an average power of 800 mW. The calculated M2 value is 1.3, the output is very stable, and the laser operates in the TEM00 mode.