Hemispherical Cavity Research Articles

Design of biomimetic substrates for long-term maintenance of alveolar epithelial cells.

There is a need to establish in vitro lung alveolar epithelial culture models to better understand the fundamental biological mechanisms that drive lung diseases. While primary alveolar epithelial cells (AEC) are a useful option to study mature lung biology, they have limited utility in vitro. Cells that survive demonstrate limited proliferative capacity and loss of phenotype over the first 3-5 days in traditional culture conditions. To address this limitation, we generated a novel physiologically relevant cell culture system for enhanced viability and maintenance of phenotype. Here we describe a method utilizing e-beam lithography, reactive ion etching, and replica molding to generate poly-dimethylsiloxane (PDMS) substrates containing hemispherical cavities that mimic the architecture and size of mouse and human alveoli. Primary AECs grown on these cavity-containing substrates form a monolayer that conforms to the substrate enabling precise control over cell sheet architecture. AECs grown in cavity culture conditions remain viable and maintain their phenotype over one week. Specifically, cells grown on substrates consisting of 50 μm diameter cavities remained 96 ± 4% viable and maintained expression of surfactant protein C (SPC), a marker of type 2 AEC over 7 days. While this report focuses on primary lung alveolar epithelial cells, our culture platform is potentially relevant and useful for growing primary cells from other tissues with similar cavity-like architecture and could be further adapted to other biomimetic shapes or contours.

Fabricating tool for ultrasonic machining using reverse engineering

ABSTRACTDeveloping tools for ultrasonic machining processes is one of the most challenging tasks, because the shape of the machined surface of the workpiece is a replica of the tool surface. In this research, using reverse engineering (RE), the tool has been designed and fabricated for the ultrasonic machining (USM) process. Zirconia is a very hard and brittle bio-ceramic material and is highly biocompatible. Nowadays, zirconia material is used for producing the acetabular cup for hip joint. In this research work, an attempt has been made to apply the RE for developing the CAD model of a USM tool from the existing hemispherical shape cavity on a zirconia workpiece. Experimental analysis has been undertaken for generating the hemispherical shape cavity on zirconia bio-ceramics with the help of these developed tools. Through a number of graphical plots, comparisons of diametrical deviation and circularity error have been made using RE and without RE. Comparisons have also been made for justifying the accuracy of the tool development by RE with respect to the initial existing hemispherical shape cavity and developed tool for USM.

Natural convection between concentric and inclined hemispherical cavities filled with Cu-water nanofluid

The hemispherical cavity is used for various applications in diverse engineering sectors. This is particularly acute for thermoregulation of electronic assemblies contained in the enclosures considered here, regardless of the shape of the heat source and the used fluid. This work quantifies and qualifies the dynamic and thermal phenomena occurring by natural convection between two concentric hemispheres. The external cupola is kept isothermal and the active internal hemisphere is an electronic assembly generating significant power during its operation. The latter lead to high Rayleigh number reaching 7.29×1010. The base (disc) of the assembly could be inclined with respect to the horizontal plane by an angle ranging from 0° (horizontal disc with dome facing upwards) to 180° (horizontal disc with dome facing downwards) depending on the application. The nanofluid used consists of water-base and copper nanoparticles, with a volume fraction varying between 0 (pure water) and 10%. The 3D numerical solution using a one-phase model is performed by means of the volume control method based on the SIMPLE algorithm. It highlights the improvement of the convective heat transfer by using this nanofluid. Calculations performed for many combinations of the Rayleigh number, inclination angle and volume fraction allowed to quantify the free convective heat transfer, presented by means of a correlation of the Nusselt-Rayleigh-Prandtl-inclination angle type.

Tunable Light–Matter Hybridization in Open Organic Microcavities

Open microcavities represent a versatile cavity design that allows the external control of internal properties such as cavity thickness and mode detuning without changing the key parameters of the cavity itself, rendering them particularly interesting for light–matter interaction experiments. Here, we demonstrate the tunability of an open microcavity with an embedded active organic layer providing parallel alignment of molecular transition dipole moments as well as strong self-absorption inside the cavity. By decreasing the cavity thickness, we observe a transition from the weak coupling regime into the strong coupling regime evidenced by the onset of avoided crossing behavior between involved modes. This change of coupling mechanism is shown for 2D (planar) as well as 0D (hemispherical) cavities.

A three-dimensional thermal model for viscoelastic polymer melt packing process in injection molding

In this study, a 3D weakly compressible viscoelastic flow model with the thermal effect is developed for simulations of the non-isothermal XPP melt packing process. The 3D multi-field coupled model is solved by the collocated finite volume CLEAR algorithm with the AVLSMART scheme. The numerical model is validated against the benchmark problem. The XPP melt packing process in a rectangular cavity is simulated, and the predicted flow-induced birefringence is in agreement with the experimental and numerical results reported in the literature. For a case with a rather complex cavity, the XPP melt packing process in a 3D hemispherical shell cavity is further simulated. The distributions of melt temperatures, flow-induced stresses as well as the corresponding rheological characteristics of XPP melt in 3D cavity are vividly presented, which are difficult to be captured by previous simulations and experiments. Especially, the present model allows the effects of melt temperature and holding pressure on the first normal stress difference and density to be studied. It is shown that with an increase in melt temperature, the absolute values of the first normal stress difference increases slightly and the density decreases gradually, while the high holding pressure improves significantly the first normal stress difference and density. Numerical results demonstrate that the present 3D thermal model is an effective tool for simulating real-world viscoelastic polymer melt packing processes.

Numerical and experimental investigation of wind effect on a hemispherical cavity receiver

In this study, a parabolic dish concentrator with a hemispherical cavity receiver was investigated under windy weather conditions. In the first section, a numerical analysis was carried out to determine an optimum structural parameter of the hemispherical cavity receiver. Two equations were numerically determined for prediction of the optimum aperture area of the cavity receiver and the maximum receiver thermal efficiency versus the optical errors in the range of 5mrad to 35mrad. In the second section, the optimized hemispherical cavity receiver was experimentally constructed, and the experimental tests were carried out in a real weather condition. The effect of the wind speed on the cavity heat losses was experimentally investigated. A correlation between the heat losses, due to the wind, and the wind speed was experimentally estimated in form of the Q̇loss,wind=59.545×Vwind+76.724. The correlation was obtained for the investigated hemispherical cavity receiver with R2=0.9477 for the side wall direction of the wind. The cavity wall temperatures show an inverse behavior with the wind speed. Also, the cavity top wall temperatures indicate higher amount than the cavity side wall temperatures. Finally, the effect of the wind speed was considered on the energy performance of the hemispherical cavity receiver. The results indicate that the wind is an effective parameter in the energy performance of the hemispherical cavity receiver. Therefore, the application of the glass cover of the hemispherical cavity receiver will be recommended.

EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF FUEL INJECTION PARAMETERS ON DIESEL ENGINE PERFORMANCE AND EMISSIONS

The climate changes and increase in global temperature are the key factors that have mainly amplified the exploration studies of changing fuel injection and other constraints of compression ignition (CI) engines for the abatement of exhaust emissions. In current study, a direct injection (DI), CI engine was run on a test bench for the performance and emission analyses using different nozzles and injection timings. During the experiments, two types of nozzles known as sac and valve covered orifice (VCO) were used with hemispherical cavity and toroidal cavity pistons, respectively. Besides an already existing set of sac type nozzles, six distinct combinations of nozzles with varying cone angles and tip penetration (protrusion) lengths (designated as 135° × 3.5 mm, 140° × 3.5 mm, 145° × 3.5 mm, 150° × 3.5 mm, 150° × 2.5 mm, and 150° × 1.5 mm) were used at three different injection timings comprising 16° before top dead center (BTDC), 13°BTDC and 10°BTDC. Experimental results reveal that VCO nozzles in toroidal combustion chamber (CC) are better than sac nozzles with hemispherical CC, and that wider cone angle nozzles at 10° BTDC give the optimum results in terms of emissions and performance, relative to those of narrower cone angles. The 150° nozzles with 1.5 mm tip penetration give abated carbon monoxide (CO), hydrocarbon (HC) and smoke emissions along with better performance characteristics such as brake specific fuel consumption (BSFC) and brake power (BP), while exhibit slightly higher oxides of nitrogen (NOx) relative to other combinations. Moreover, the same combination also proves to be effective on emission control at 8 mode steady-state cycle.

Spectroscopy and visible laser operations of a μ-PD grown Pr3+ :LiYF4 single-crystal fiber

We report on the growth and visible laser operations of a single-crystal fiber of Pr3+ :LiYF4 (Pr:YLF), grown by the micro-pulling-down method (μ-PD). We performed spectroscopic analyses on the crystal and compared the results with a Czochralski-grown sample of the same material. These analyses proved the high optical quality of the fiber. Using a hemispherical cavity and pumping the crystal with an InGaN-based laser diode, we achieved laser emission in the orange, red and deep red regions. We measured the slope efficiencies of three transitions and studied the propagation of output beams. To the best of our knowledge, these are the first laser operations in a Pr:YLF single-crystal fiber grown by this method.

3D printed bandpass filters using compact high‐ Q hemispherical resonators with improved out‐of‐band rejection

RF design and implementation of ceramic-filled resin-based 3D printed millimetre-wave bandpass filters (BPFs) using a new class of compact high-quality-factor hemispherical cavity resonators are addressed. Design concept of the hemispherical resonator is discussed for BPF applications in both X and Ka bands. For validation purpose, the Ka-band fourth-order BPF is fabricated with a high-temperature-resistant ceramic-filled resin using a fast and low-cost stereolithography-based 3D printing technique, and its surface metallisation is realised by employing electroless copper/silver plating. The proposed BPF's geometrical configuration contributes to a significantly improved out-of-band rejection. The RF-measured results demonstrate the Ka-band BPF an insertion loss of 0.43−0.9 dB from 31.52 to 32.42 GHz, a passband return loss mostly better than 15 dB, and a small frequency shift of about 0.06%.

Spectroscopic properties and continuous-wave laser operation of Er3+:Yb3+:LaMgB5O10 crystal

A bulk crystal of Er3+:Yb3+:LaMgB5O10 was grown successfully by the top seeded solution growth (TSSG) method. The spectroscopic characterization of this material, including the polarized absorption and fluorescence spectra and the fluorescence decay curve, were recorded. The fluorescence quantum efficiency of the 4I13/2 level of Er3+ ions and the efficiency of energy transfer from Yb3+ to Er3+ ions were estimated. Continuous-wave laser output of 160 mW at 1567 nm was realized under the absorbed pump power of 3.1 W in a hemispherical cavity. When the output coupler transmission was 1.7% the absorbed pump threshold was 1.5 W and the slope efficiency of the laser was 10.1%. The results show that Er3+:Yb3+:LaMgB5O10 crystal is a promising laser material.

Focusing metasurface quantum-cascade laser with a near diffraction-limited beam.

A terahertz vertical-external-cavity surface-emitting-laser (VECSEL) is demonstrated using an active focusing reflectarray metasurface based on quantum-cascade gain material. The focusing effect enables a hemispherical cavity with flat optics, which exhibits higher geometric stability than a plano-plano cavity and a directive and circular near-diffraction limited Gaussian beam with M2 beam parameter as low as 1.3 and brightness of 1.86 × 106 Wsr-1m-2. This work initiates the potential of leveraging inhomogeneous metasurface and reflectarray designs to achieve high-power and high-brightness terahertz quantum-cascade VECSELs.

Simulation of plasma filled hemispherical cavity as dielectric resonator antenna

Plasma antennas are becoming an increasingly interesting research topic because of their uncommon characteristics. They are highly configurable, can be turned on and off rapidly, and exhibit lower thermal noise compared to metal antennas. In recent years, research has been conducted on cylindrical plasma columns sustained by DC, RF or microwave field, and their application as leaky wave antennas or as regular monopole antennas.Dielectric resonator antennas (DRA) with high dielectric permittivity are known for their small size and excellent operating characteristics for modern mobile communications (WiMAX, LTE). Hemispherical dielectric resonator antennas are characterized by simple shape, high radiation efficiency and wide bandwidth. Hemispherical DRA with a low density weakly ionized plasma as dielectric material will combine the positive features of plasma and dielectric antennas, and is particularly interesting, as antennas of this type have not been studied yet. The hemispherical plasma antenna is simulated with Ansoft HFSS in the microwave S-band. Obtained radiation pattern and bandwidth show the advantages of hemispherical plasma antennas for future communication technology.

Fabrication of Micro-Lens Array Obtained by Anisotropic Wet Etching of Silicon

This paper presents the fabrication of a micro-lens array surface with a single-mask process and two etching steps with KOH water solution. Numerical analysis of optics was used to determine the optimal design parameters such as curvature sagitta and radius. The dimension of each lens is 20μm x 20μm. We used anisotropic etching of <100> silicon through a circular and squar mask to produce a pyramidal pit formed by four (111) planes. The oxide mask is stripped and the immersion of the sample in the etchant solution favors the etching of (411) plane transforming the pit into a smooth hemispherical cavity. An intermediate stage exists when a wider 19.470 <411> - face pyramid replaces the initial 54.740 inverted pyramid. The dependence of surface roughness on concentration and temperature of KOH is investigated in the range of 25%-40% and 60°C-80°C, respectively, and compared between them. The surface profiles and roughness was characterized by AFM. The etching depth and radius of micro-lens array was obtained from the SEM images and AFM data. Also, the array of concave depressions was directly used as a mould for replication of KER-2500 transparent polymeric silicon from Shin-Etsu with a refractive index n=1.41. The perfectly matched array of micro-lenses can be detached from substrate and used as a local solar concentrator. Optical properties such as the focal length of the plano-convex micro-lens array, obtained by replication, are measured and analyzed.

First-principles definition and measurement of planetary electromagnetic-energy budget.

The imperative to quantify the Earth's electromagnetic-energy budget with an extremely high accuracy has been widely recognized but has never been formulated in the framework of fundamental physics. In this paper we give a first-principles definition of the planetary electromagnetic-energy budget using the Poynting-vector formalism and discuss how it can, in principle, be measured. Our derivation is based on an absolute minimum of theoretical assumptions, is free of outdated notions of phenomenological radiometry, and naturally leads to the conceptual formulation of an instrument called the double hemispherical cavity radiometer (DHCR). The practical measurement of the planetary energy budget would require flying a constellation of several dozen planet-orbiting satellites hosting identical well-calibrated DHCRs.

3D-printed polylactic acid supports for enhanced ionization efficiency in desorption electrospray mass spectrometry analysis of liquid and gel samples

The potential of 3D printing technology was here exploited to prepare tailored polylactic acid (PLA) supports for desorption electrospray ionization (DESI) experiments. PLA rough solid supports presenting wells of different shape (i.e. cylindrical, cubic and hemispherical cavities) were designed to accommodate samples of different physical state.The potentials of such supports in terms of sample loading capacity, sensitivity, signal stability were tested by analysing a peptide (i.e. insulin) and an aminoglycoside antibiotic (i.e. gentamicin sulphate) from solution and a chitosan-based gel. The results obtained were compared with those obtained by using a traditional polytetrafluoroethylene (PTFE) support and discussed.By using PLA support on the flat side, signal intensity improved almost twice with respect to PTFE support, whereas with spherical wells a five times improved signal sensitivity and good stability (RSD<6%) were obtained for the analysis of two model molecules. Limits of detection were in the 3–10nM range and linearity was demonstrated for both analytes in the 0.05–0.5μM range for semi-quantitative or quantitative purposes.The use of a well and the set-up of optimal source parameters allowed the analysis of samples in a gel state with good precision (RSD<10%) and accuracy (86±6–102±9%), otherwise difficult to analyse on a flat smooth surface.These findings are of great interest and stimulus to exploit the advantages of 3D printing technology for the development of devices for a DESI source, presenting different shapes or configuration as a function of the sample types.

Microstructured Air Cavities as High-Index Contrast Substrates with Strong Diffraction for Light-Emitting Diodes.

Two-dimensional high-index-contrast dielectric gratings exhibit unconventional transmission and reflection due to their morphologies. For light-emitting devices, these characteristics help guided modes defeat total internal reflections, thereby enhancing the outcoupling efficiency into an ambient medium. However, the outcoupling ability is typically impeded by the limited index contrast given by pattern media. Here, we report strong-diffraction, high-index-contrast cavity engineered substrates (CESs) in which hexagonally arranged hemispherical air cavities are covered with a 80 nm thick crystallized alumina shell. Wavelength-resolved diffraction measurements and Fourier analysis on GaN-grown CESs reveal that the high-index-contrast air/alumina core/shell patterns lead to dramatic excitation of the low-order diffraction modes. Large-area (1075 × 750 μm(2)) blue-emitting InGaN/GaN light-emitting diodes (LEDs) fabricated on a 3 μm pitch CES exhibit ∼39% enhancement in the optical power compared to state-of-the-art, patterned-sapphire-substrate LEDs, while preserving all of the electrical metrics that are relevant to LED devices. Full-vectorial simulations quantitatively demonstrate the enhanced optical power of CES LEDs and show a progressive increase in the extraction efficiency as the air cavity volume is expanded. This trend in light extraction is observed for both lateral- and flip-chip-geometry LEDs. Measurements of far-field profiles indicate a substantial beaming effect for CES LEDs, despite their few-micron-pitch pattern. Near-to-far-field transformation simulations and polarization analysis demonstrate that the improved extraction efficiency of CES LEDs is ascribed to the increase in emissions via the top escape route and to the extraction of transverse-magnetic polarized light.

High-density ordered Ag@Al2O3 nanobowl arrays in applications of surface-enhanced Raman spectroscopy

In this paper, we demonstrate a high-performance surface-enhanced Raman scattering (SERS) substrate based on high-density ordered Ag@Al2O3 nanobowl arrays. By ion beam etching (IBE) the anodized aluminum oxide (AAO) and subsequent Ag coating, ordered Ag@Al2O3 nanobowl arrays were created on the Si substrate. Unlike the ‘hot spots’ generated between adjacent metallic nanostructures, the Ag@Al2O3 nanobowl introduced ‘hot spots’ on the metal boundary of its hemispherical cavity. Based on the analysis of SERS signals, the optimized SERS substrate of Ag@Al2O3 nanobowl arrays had both high sensitivity and large-area uniformity. A detection limit as low as 10−10 M was obtained using chemisorbed p-thiocresol (p-Tc) molecules, and the SERS signal was highly reproducible with a small standard deviation. The method opens up a new way to create highly sensitive SERS sensors with high-density ‘hot spots’, and it could play an important role in device design and corresponding biological and food safety monitoring applications.

PDMS-based two-axis inclinometer with a 360-degree measuring range

In this study, we fabricated an electrolytic tilt sensor based on a unique poly(dimethylsiloxane) (PDMS) structure, which enables the successful implementation of a 360° dual-axis inclination angle measurement. The fabricated electrolytic tilt sensor consists of two parts: symmetric hemispherical PDMS cavities with detecting electrodes, and a wire-shaped carbon nanotube (CNT)-PDMS composite common electrode. The proposed electrolytic tilt sensor overcomes the limitations that have been previously reported. Specifically, it not only expands the operating range to 360°, but it also significantly increases the device response and sensitivity to 0.17s and 22mVrms/degree, respectively. We verified the stability of the proposed sensor and obtained a standard deviation (σ) of approximately 0.014. Experimental results confirm that the device is sufficient for a variety of tilt angle measurement applications by providing a measurement option that is efficient, cost effective, and does not require complex fabrication processes.

Numerical investigations on shock oscillations ahead of a hemispherical shell in supersonic flow

A clear understanding of the mechanism responsible for large amplitude shock pulsations ahead of a hemispherical cavity in supersonic flow is presented for the first time in this article. This has applications in supersonic parachute decelerators during the atmospheric descent stage of aerospace vehicles. A cell-centered finite volume code FaSTAR is used to solve the full Navier–Stokes equations on a hemispherical shell facing a Mach 4.0 supersonic free stream. The numerical method is validated against earlier experimental results. First, Flow Configuration A appears consisting of an axisymmetric shock that undergoes low-amplitude oscillations. This flow transitions to Flow Configuration B that has an asymmetric shock structure and undergoes large-amplitude non-stationary shock pulsations. The shock stand-off distance in Flow Configuration B is 1.65 times that in Flow Configuration A. The generation of vortices from the curved shock, amplification of vortices of one kind due to the dynamics of the cavity flow, and further interaction of these amplified vortices with the shock in a loop causes the large-amplitude shock pulsations. The oscillation frequencies as determined from cavity pressure and shock stand-off distance signals extracted from the unsteady results are 1.26 kHz during Flow Configuration A, and 859 and 863 Hz during the non-stationary pulsations of Flow Configuration B. The Helmholtz resonator model predicts quite accurately the frequency of Flow Configuration A (1.27 kHz), and to a good extent the frequency in Flow Configuration B (916.7 Hz).

Experimental studies of ultrasonic machining on hydroxyapatite bio-ceramics

Hydroxyapatite bio-ceramics are used for producing implants for bio-medical applications. The generation of hemispherical shaped cavity on hydroxyapatite bio-ceramic is highly demanded for making hip joint. Ultrasonic machining is suitable for the machining of all kind of hard and fragile materials, which are electrically non-conducting. This paper is aimed to design and develop a tool and holding arrangement in ultrasonic machining (USM) for generating hemispherical shaped cavity on hydroxyapatite bio-ceramic which is highly demanded for hip joint replacement. This paper also includes the study of the influences of process parameters such as abrasive grain diameter, abrasive slurry concentration, tool feed rate and power rating on material removal rate, diametrical deviation, and circularity error during ultrasonic machining. From the basic parametric studies, it is observed that the abrasive grain diameter, power rating, and tool feed rate are the most important parameters, which have greater influence on the material removal rate (MRR), diametrical deviation, and circularity error of hemispherical cavity on hydraxyapatite bio-ceramics. It is also concluded that the hemispherical shaped cavity on hydroxyapatite bio-ceramics with dimensional accuracy can be generated by USM with the aid of developed tool geometry and proper control of process parameters during ultrasonic machining.