Arrangement Of Cavities Research Articles

Flow and heat transfer performance of microchannel heat sinks with circular concave cavities and ribs for water cooling LEDs

ABSTRACT The poor heat dissipation of LED light sources limits their applications in plant factories. This paper combines a microchannel heat sink (MHS) with circular concave cavities and ribs with the water irrigation system of an LED plant factory to develop water-cooled LEDs. By using this approach, four types of MHSs were designed: circular concave cavities (circular), circular concave cavities and single-sided ribs (circular-single), circular concave cavities and odd-symmetric ribs (circular-odd), and circular concave cavities and double symmetric ribs (circular-double). The influence of the arrangement of circular concave cavities and ribs on the flow and heat transfer performance was numerically investigated by ANSYS Fluent 21.0 R1. Corresponding MHSs with circular concave cavities and ribs were manufactured, and an experimental platform was built to experimentally verify the numerical results. The results showed that a circular concave cavity in the microchannel caused the fluid to form a secondary flow, which led to the continuous destruction and reconstruction of the flow and thermal boundary layer in the microchannel. This contributed to heat and mass transfer, while the presence of ribs altered the flow direction of the fluid and enhanced mass and heat transfer within the cavities. The pressure drop at the inlet and outlet of the MHS increased in the case of circular concave cavities and ribs as the inlet flow rate increased. Compared with MHSs with circular concave cavities, the ribs increased the pressure drop at the inlet and outlet. The inlet and outlet pressure drop of MHS with circular concave cavities and double-symmetric ribs was the highest, followed by MHS with circular concave cavities and odd-symmetric ribs, and the smallest was the MHS with circular concave cavities and single-sided ribs. As the inlet flow rate increased from 10 ml/min to 60 ml/min, the pressure drop between the inlet and outlet of the MHS with circular concave cavities increased from 22.54 Pa to 165.98 Pa (an increase of 143.44 Pa); the pressure drop of the MHS with circular concave cavities and single-sided ribs increased from 24.72 Pa to 187.31 Pa (an increase of 162.59 Pa); the pressure drop of the MHS with circular concave cavities and odd-symmetric ribs increased from 27.92 Pa to 212.12 Pa (an increase of 184.20 Pa) and that of the MHS with circular concave cavities and double symmetric ribs increased from 29.32 Pa to 221.21 Pa (an increase of 191.89 Pa). Under the same inlet flow rate and LED chip input power, the cooling water outlet temperature of MHS with circular concave cavities and double symmetric ribs was the highest, followed by MHS with circular concave cavities and odd-symmetric ribs, MHS with circular concave cavities and single-sided ribs, and MHS with circular concave cavities was the lowest. These results indicated that the heat transfer performance of MHS with circular concave cavities and double-symmetric ribs was the best, followed by MHS with circular concave cavities and odd-symmetric ribs, and MHS with circular concave cavities and single-sided ribs. The MHS with circular concave cavities had the worst heat transfer performance. The outlet temperature of the MHS with concave cavities and ribs reaches the highest value at the inlet flow rate of 30 ml/min. At this flow rate, the outlet temperature is 343.89 K for the MHS with circular concave cavities, 344.73 K for the MHS with circular concave cavities and single-sided ribs, 346.53 K for the MHS with circular concave cavities and odd-symmetric ribs; and 347.58 K for the MHS with circular concave cavities and double symmetric ribs.

Features of radiological manifestations in the diagnosis of nontuberculous mycobacteriosis. Literature review Сlinical observation

Purpose of the study. The purpose of this literature review is to determine the radiographic features in the diagnosis of non-tuberculous mycobacteriosis (NTMB) and to assess the possibility of radiological diagnosis of a combination of tuberculosis and non-tuberculous mycobacteriosis of the lungs in a patient with HIV infection.Materials and methods. A review of the literature on the bases of scientific articles PubMed, ELibrary and Google Scholar. Attention was focused on full-text articles. The article presents a clinical observation of a patient being treated at the Clinical TB Dispensary in Omsk from 2019 to 2022 with a diagnosis of disseminated pulmonary tuberculosis, bilateral, in the infiltration phase, tuberculous spondylitis ThVII–IX, complicated by a paravertebral abscess.Results. The radiological changes characteristic of NTMB are: lesion of the right middle and lingual lobes of the lungs with the presence of diffuse bronchiectasis, changes in the type of “tree in the kidneys”, compaction of lung tissue by the type of “frosted glass” with the presence of centrilobular nodules, asymmetric small dense foci with peribronchial location, apical location of thin-walled cavities with thickening of the costal pleura, as well as foci of inflammatory infiltration. The absence of specific symptoms for this pathology requires further research in this area. The identification of characteristic radiological features will speed up the diagnosis of infection and determine the correct management tactics for patients.Conclusion. The radiosemiotics of NTMB is characterized by a large variability of manifestations. The most informative method of radiation diagnosis of NTMB is multispiral computed tomography (MSCT). Thanks to MSCT, a radiologist has the opportunity to accurately assess the localization and nature of foci, as well as assess the dynamics and prevalence of the process. The most characteristic radiological symptoms are the defeat of the right middle and lingual lobes of the lungs with the presence of diffuse bronchiectasis, changes in the type of “tree in the kidneys”, compaction of lung tissue by the type of “frosted glass” and the presence of centrilobular nodules, asymmetric small dense foci with peribronchial arrangement, apical arrangement of thin-walled cavities with thickening of the costal pleura, as well as foci inflammatory infiltration. The absence of specific symptoms for this pathology requires further research in this area. The identification of characteristic radiological features will speed up the diagnosis of infection and determine the correct management tactics for patients.

Simultaneous single photon counting and ion channel recording from free-standing lipid bilayers on a microstructured array.

Fluorescence microscopy and, in particular, single molecule optical spectroscopy is of great potential value in characterizing the structural dynamics of membranes and membrane proteins. A particular challenge is to combine such high-resolution optical measurements with high-resolution voltage clamp electrical recordings that can provide direct information on single ion channel gating a block by drugs and analytes. Here, we report on the use of a novel chip-based, 2 × 2 arrangement of microelectrode cavities with borosilicate glass optical windows which facilitates optical access on an inverted microscope with water or oil-immersion objectives of high numerical aperture to horizontal free-standing lipid membranes, while controlling membrane voltage and recording currents using individual micropatterned, ring-shaped Ag/AgCl-electrodes to perform time-resolved single photon counting on free-standing membranes spanning sub-nanoliter cavities. Single channel activity induced by the fluorescently labelled pore-forming peptide ceratotoxin A was simultaneously acquired. This device allows for rapid formation of four membranes that are simultaneously monitored electrically using a four-channel amplifier and can be sequentially optically addressed, greatly reducing the time needed for successful experimentation. During our experiments, we noted autofluorescence of the borosilicate to be a limiting factor for wide-field low-intensity fluorescence recording, but this can likely be circumvented by using quartz glass instead. In summary, the novel device increases the likelihood of realizing the long standing ambition to correlate structural and functional dynamics of single membrane proteins on the single molecule level.

Structure and interface engineering on polypyrrole-deposited conductive paper originating from nature wood enables high performance flexible all-solid-state supercapacitors

Paper is an ideal substrate for manufacturing flexible electrodes because of its lightweight, inherent mechanical flexibility, and unique structure. However, the traditional bottom-up method of manufacturing paper-based electrode is time-consuming and the active material is easy to fall off. Here, we report a polypyrrole-deposited conductive paper (PCP), which is fabricated by chemical treatment, mechanical compression, and chemical polymerization of natural wood. The post densification process eliminates the vertical arrangement of wood cell cavities, and the formed wood fiber/multi-walled carbon nanotubes hybrid conductive network has high flexibility. The further deposited polypyrrole (PPy) conductive layer can effectively boost the ion transport between electrode/electrolyte interface and increase the active center of interface reaction. Based on the well-designed electrode structure and good interfacial reaction kinetics, the resulting PCP with a PPy mass loading of only 2.4 mg·cm−2 indicates a high areal capacitance of 275.8 mF cm−2 at 20 mV·s−1 and good cycling stability. All-solid-state symmetric supercapacitor exhibits capacitance of 308.3 mF·cm−2. This structure and interface design concept show a promising method for preparing high-performance and scalable biomass-based flexible electronic devices.

Second harmonic generation from nano cavities milled in thin aluminum film

Second harmonic generation (SHG) is forbidden for centrosymmetric materials such metals. Yet, symmetry can be broken by introducing plasmonic nano-structures which lead to enhancement of the electromagnetic field at both the fundamental and the SH frequencies. Using non-linear microscopy, we experimentally demonstrate enhanced SHG from isosceles triangular cavities (~215 nm side length, 200 nm base) milled in thin aluminum film. Upon strong interaction between the cavities, they behave as a single unit and response in a coherent manner, i.e. SHG is observed from the coupled system. The hybridization between the cavities is not only dependent on the distance between them, but their spatial arrangement is found to be a crucial parameter. That is, the SHG efficiency can be enhanced upon different arrangement of the same cavities, holding the same distance between them. We characterize those cavities also by cathodoluminescence and show that the structure support plasmonic modes both at the fundamental and the SH frequencies.

Redesigning and numerical simulation of gating system to reduce cold shut defect in submersible pump part castings

Gating system design is an essential element in casting that significantly affects the melt's molten metal flow behaviour, heat transfer, and solidification. Improper gating system leads to pouring-related defects like cold shut, misrun, etc. Submersible pump-bearing block castings produced in one of the leading foundries are rejected due to a cold shut defect. It was identified that the improper gating system is the probable cause for rejection. The bearing block and the existing gating system were modelled in 3D modelling software, and the molten metal flow behaviour of casting was simulated with casting simulation software. Based on the simulation results, the existing gating system was redesigned following established empirical relations. The component with the revised gating system was analysed for flow behaviour through simulation with the software. With the revised gating system, elimination of cold shut is observed, and the revised gating design is recommended to the industry for implementation. The effectiveness of the revised gating system is also validated with pump diffuser casing, which has similar geometrical and material characteristics. The simulation results and experimental validation showed a reduction in flow and surface defects. Appropriate design of the gating system and balanced arrangement of cavities in the gating system are noted to reduce the flow and surface-related defects. It is observed that with the revised gating systems, the percentage of rejection is reduced from 28.36% to 2.34% and 23.43% to 2.45% for the bearing block and pump diffuser casing respectively.

Developing Broadband Microstrip Patch Antennas Fed by SIW Feeding Network for Spatially Low Cross-Polarization Situation.

A stacked multi-layer substrate integrated waveguide (SIW) microstrip patch antenna with broadband operating bandwidth and low cross-polarization radiation is provided. A complete study on the propagating element bandwidth and cross polarization level is presented to demonstrate the importance of the design. The proposed antenna includes three stacked printed circuit board (PCB) layers, including one layer for the radiating 2 × 2 rectangular patch elements and two SIW PCB layers for the feeding network. There are two common methods for excitation in cavity-backed patch antennas: probe feeding (PF) and aperture coupling (AC). PF can be used to increase the bandwidth of the antenna. Although this method increases the antenna’s bandwidth, it produces a strong cross-polarized field. The AC method can be used to suppress cross-polarized fields in microstrip patch antennas. As microstrip patch antennas are inherently narrowband, the AC method has little effect on their bandwidth. This paper proposes an antenna that is simultaneously fed by AC and PF. As a result of this innovation, the operating bandwidth of the antenna has increased, and cross-polarization has been reduced. Actually, the combination of probe feeding and aperture coupling schemes leads to achieving a broadband operating bandwidth. The arrangement of radiator elements and cavities implements a mirrored excitation technique while maintaining a low cross-polarization level. In both numerical and experimental solutions, a less than −30 dB cross-polarization level has been achieved for all of the main directions. A fractional impedance bandwidth of 29.8% (10.55–14.25 GHz) for < −10-dB is measured for the proposed array. Simulated and measured results illustrate good agreement. Having features like low cost, light weight, compactness, broadband, integration capabilities, and low cross-polarization level makes the designed antenna suitable for remote-sensing and satellite applications.

Improved low-frequency sound absorption of porous silicone rubber resonance sheet with periodic cavities

Since the development of advanced sound absorption material is highly critical in noise control applications, anechoic coatings, and acoustic metamaterials, both fabrication technology and structure design are significant in the achievement of broadband and strong absorption performance in the low sound frequency range. In this work, the silicone rubber resonance absorption sheet with periodic cavities is prepared via inserting cylindrical steel strips with different diameters into the non-vulcanized colloid. Effects of size and arrangement of cavities on the sound absorption properties, as well as the corresponding mechanical properties, are investigated and discussed. Results indicate that periodic pattern designs could further improve the low-frequency sound absorption performance of silicone rubber foams, and increasing the cavity diameter could significantly improve the sound absorption efficiency of the prepared samples in the middle- and low-frequency range from 125 to 2000 Hz. Particularly, increasing the number of the layered cavities could also improve the sound absorption efficiency. The consumption of sound energy in the prepared silicone rubber resonance sheet is discussed, which could be attributed to the synergistic effect in different spatial scales.

МОДЕЛЮВАННЯ ПРОЦЕСУ ВЗАЄМОДІЇ ІМПУЛЬСНОГО СТРУМЕНЯ ІЗ ЗАГОТОВКОЮ ПРИ ЕЛЕКТРОГІДРАВЛІЧНОМУ НА-ВАНТАЖЕННІ

The eg-stamping of thin-leaf-sized parts has shown its technical and economic efficiency, including the ability to receive parts of ultrahon-thread accuracy. At the same time, the workpieces are loaded on the eg-presses of large intensive energy (up to 500 kJ), which have the possibility of space-time loading control. Such management is carried out using multi-terminated discharge blocks in which dozens of discharge cavities are combined into one. The controlled parameters can be the electrical parameters of tens of discharge circuits of the current pulse generator, the volume and step of the arrangement of the discharge cavities, their height to the workpiece, as well as the sequence of discharges in time (simultaneous or with a shift in the time of EG-discharges in adjacent discharge cavities). The choice of rational ranges of these parameters is impossible without numerical simulation of processes occurring in the discharge volume of the entire block.In the simulation, the processes of heat power is comprehensively considered with the EG-discharge, the formation and propagation of the vapor-gas bubble, which generates a flooded stream of liquid, and deforming the supple billet when exposed to such a jet.The results of numerical experiments in the LS-DYNA environment using the ALE method with the EG-discharge in a single bit (submersible) chamber, in two and three neighboring conditions with different variable conditions are set: the distance from the discharge zone to the workpiece (discharge distance) and the displacement of the time of two and three discharges in the adjacent discharges. As compared parameters were selected: movement of the billet and their speed, the distribution of deformations on the surface of the workpiece and the work of deformation. The adequacy of the model of the real process is shown. An energy-efficient energy-generating cell is proposed for generating EG-discharges from a multi-mounted pulse current generator.

Acoustically-actuated bubble-powered rotational micro-propellers

Bubble-powered acoustic microsystems span a plethora of applications that range from lab-on-chip diagnostic platforms to targeted interventions as microrobots. Numerous studies strategize this bubble-powered mechanism to generate autonomous self-propulsion of microrobots in response to high frequency sound waves. Herein, we present two micro-propeller designs which contain an axis-symmetric distribution of entrapped bubbles that vibrate to induce fast rotational motion. Our micro-propellers are synthesized using 3D Direct Laser Writing and chemically-functionalized to selectively trap air bubbles at their micro-cavities which function as propulsion units. These rotational acoustic micro-propellers offer a dual advantage of being used as mobile microfluidic mixers, and as autonomous microrobots for targeted manipulation. With regards to targeted manipulation, we demonstrate magneto-acoustic actuation of our first propeller design that can be steered to a desired location to perform rotational motion. Furthermore, our second propeller design comprises of a helical arrangement of bubble-filled cavities which makes it suitable for spatial micro-mixing. Our acoustic propellers can reach speeds of up to 400 RPM (rotations per minute) without requiring any direct contact with a vibrating substrate in contrast to the state-of-the-art rotary acoustic microsystems.

Concentrating and black hole like structures by elastic metamaterials with acoustic cavities under active feedback control

In the underwater sonar or similar devices where the high pressure field is required, the concentrating and black hole like structures have important applications in harvesting energy systems of elastic waves. In this work, a new kind of active elastic metamaterials with cavities and an acoustic concentrator are presented. By the feedback control gain of piezoelectric diaphragms, we can obtain both the controllable effective bulk modulus and density within a wide frequency range. Based on the coordinate transformation method and by the feedback control on the periodic arrangement of acoustic cavities, an acoustic concentrator with multilayered alternative homogeneous materials can be achieved. Numerical results show that the acoustic wave is perfectly limited within the core region of the concentrator, which can enhance the acoustic energy. These characteristics with the tunable effective bulk modulus and density within a very wide frequency range are expected to be helpful for the design of practical acoustic concentrators.

Ionic Clathrate Hydrates of Tetra-n-Butylammonium Nitrate (TBANO3) and Mixed TBA(NO3,OH): Novel Superstructures of Tetragonal Structure I

The structures of an ionic clathrate hydrate of tetra-n-butylammonium nitrate TBANO3·26.7H2O and mixed TBA(NO3)1−x(OH)x·(31.5 − x)H2O hydrate obtained from a mixture of tetra-n-butylammonium nitrate and tetra-n-butylammonium hydroxide are determined by single crystal X-ray diffraction. These structures are new types of superstructures based on classical tetragonal structure I with four- and twofold unit cells volumes for TBANO3·26.7H2O and TBA(NO3)1−x(OH)x·(31.5 − x)H2O respectively. The superstructures form as a result of ordering in the arrangement of multicompartment cavities of the water-anionic framework. A TBA cation is displaced from the center of combined cavities due to the anisotropic environment of the anions, which leads to an additional symmetry reduction. The modes of the nitrate anion incorporation into the water framework of ionic clathrate hydrates are determined for the first time.

Body cavities in bryozoans: Functional and phylogenetic implications.

Based on morphological evidence, Bryozoa together with Phoronida and Brachiopoda are traditionally combined in the group Lophophorata, although this view has been recently challenged by molecular studies. The core of the concept lies in the presence of the lophophore as well as the nature and arrangement of the body cavities. Bryozoa are the least known in this respect. Here, we focused on the fine structure of the body cavity in 12 bryozoan species: 6 gymnolaemates, 3 stenolaemates and 3 phylactolaemates. In gymnolaemates, the complete epithelial lining of the body cavity is restricted to the lophophore, gut walls, and tentacle sheath. By contrast, the cystid walls are composed only of the ectocyst-producing epidermis without a coelothelium, or an underlying extracellular matrix; only the storage cells and cells of the funicular system contact the epidermis. The nature of the main body cavity in gymnolaemates is unique and may be considered as a secondarily modified coelom. In cyclostomes, both the lophophoral and endosaccal cavities are completely lined with coelothelium, while the exosaccal cavity only has the epidermis along the cystid wall. In gymnolaemates, the lophophore and trunk cavities are divided by an incomplete septum and communicate through two pores. In cyclostomes, the septum has a similar location, but no openings. In Phylactolaemata, the body cavity is undivided: the lophophore and trunk coeloms merge at the bases of the lophophore arms, the epistome cavity joins the trunk, and the forked canal opens into the arm coelom. The coelomic lining of the body is complete except for the epistome, lophophoral arms, and the basal portions of the tentacles, where the cells do not interlock perfectly (this design probably facilitates the ammonia excretion). The observed partitioning of the body cavity in bryozoans differs from that in phoronids and brachiopods, and contradicts the Lophophorata concept.

Pressure evolution inside a cork stopper under vacuum

A cork stopper maybe described by a 3D array of microcavities, which is a 3D arrangement of small cavities interconnected by tiny restrictions. Upon a step pressure change gas slowly flows through the restrictions from the microcavities to the exterior. In this work, we describe a technique to calculate the pressure evolution inside the array and the total gas flow. It is based on electrical analogies and uses a SPICE simulation software to solve large arrays. We reveal how to convert orthogonal 3D arrays in 1D arrays based on symmetry considerations, allowing us to simulate very large systems. We then apply our technique to a cork stopper to calculate the pressure evolution in the inner cell when the stopper is subjected to vacuum. We also describe an experiment to measure the characteristic time constant of a cork stopper and we compare the experimental results with those obtained from our simulations.

Multiple spheroidal cavities with surface stress as a model of nanoporous solid

The multiple cavity model of nanoporous solid has been developed which takes into account the elastic stiffness of matrix solid, porosity, shape, size and arrangement of cavities as well as the effects of their interaction. To describe the pertinent to nano level size effect of the stress field and effective stiffness, the Gurtin–Murdoch model that includes both surface tension and surface stiffness has been applied. A complete semi-analytical solution to the model problem has been obtained by the multipole expansion method. The displacement perturbation field induced by each cavity is expanded over a set of the vector solutions of Lamé equation in spheroidal basis. Expansion of the displacement and stress fields in terms of the vector surface harmonics reduces the surface conditions to an infinite linear system for the multipole strengths. The superposition principle and re-expansion formulas for the partial vector solutions extend this theory to problems involving multiple cavities. The method provides accurate evaluation of the stress field with the interaction effects taken into account. Also, the derived solution constitutes a mathematical background of the modified Maxwell homogenization scheme. The stiffness tensor of nanoporous solid is found by equating the induced dipole moment of equivalent inclusion to the total dipole moment of individual cavities. Numerical study demonstrate an accuracy and computational efficiency of the developed approach and shows quite a significant combined effect of the cavity shape and surface tension and stiffness on the stress field and macroscopic stiffness of nanoporous solid.

Silicon slot waveguide Fano resonator.

The growing interest for Fano resonators during the past decade is due to the narrow line shape observable in their optical spectra. The drastic phase shift occurring at the resonance yields a steep drop from a high to low amplitude. Fano resonances can be obtained by a combination of nanostructures. Such a system is extremely sensitive in terms of both geometrical parameters and environmental conditions. Here we study a complex arrangement of photonic crystal cavities and slot waveguides on a silicon chip. Our structure, composed of several cavities in parallel, has a particular response superimposing a shallow photonic bandgap and a resonance with a Fano line shape. It provides a low noise and a clear asymmetric resonance. We demonstrate it experimentally and show the potential of such a device for sensing. A sensitivity of 92 nm/RIU is measured.

2D Arrangement of Polymer Microsphere Photonic Cavities Doped with Novel N‐Rich Carbon Quantum Dots Display Enhanced One‐ and Two‐Photon Luminescence Driven by Optical Resonances

AbstractLuminescent carbon dots (CDs) are emerging as a potential eco‐friendly alternative to standard metal‐based semiconductor quantum dots. A solvatothermal method to prepare crystalline, nitrogen‐rich, surface‐passivated, and rare excitation wavelength‐independent green‐emitting (λmax ≈ 522 nm in solution and 536 nm in solid) CDs from a pyridine diamine precursor in ethanol solvent is reported here. In comparison to a neat thin film of CDs, a film of CD‐doped polystyrene microspheres (PS‐CDs) displays a remarkable enhancement of the photoluminescence emission intensity driven by optical cavity effect of the composite microspheres. Apart from downconversion one‐photon luminescence, upon excitation with 800 nm femtosecond pulse laser, pure CDs and PS‐CDs exhibit enhanced upconversion two‐photon luminescence in the range of about 410–580 nm.

Analysis of field synergy principle and the relationship between secondary flow and heat transfer in double-layered microchannels with cavities and ribs

The characteristic of flow and heat transfer in double-layered microchannels with cavities and ribs is investigated numerically. The intensity of secondary flow (Se) and field synergy principle are used to evaluate the heat transfer performance. The results show that the effect of arrangement of cavities and ribs on friction factor and Nusselt number is obviously. The opposite cavities and aligned ribs aside the microchannel wall (Channel C) exhibit the highest intensity of secondary flow, thus resulting in the highest Nusselt number and pressure drop simultaneously. From the view point of field synergy principle, Channel C has the smallest value of field synergy angle β and the highest value of field synergy number Fc, which indicates the best synergy relationship between velocity and temperature fields. Lastly, a thermal enhanced factor is used to evaluate the comprehensive effect of flow friction and heat transfer. The thermal enhanced factor of Channel C increases with Se firstly and then decreases. The offset cavities and ribs aside the microchannel wall (Channel B) shows the best comprehensive effect in the range of Reynolds number and Se studied here. Therefore, Reasonable geometric design of double-layered microchannels must be considered to enhance heat transfer and decrease pressure drop as well.

Accuracy of the fast multipole boundary element method with quadratic elements in the analysis of 3D porous structures

In this work, a fast multipole boundary element method for 3D elasticity problem was developed by the application of the fast multipole algorithm and isoparametric 8-node boundary elements with quadratic shape functions. The problem is described by the boundary integral equation involving the Kelvin solutions. In order to keep the numerical integration error on appropriate level, an adaptive method with subdivision of boundary elements into subelements, described in the literature, was applied. An extension of the neighbour list of boundary element clusters, corresponding to near-field computations, was proposed in order to reduce the truncation error of expansions in problems with high stress concentration. Efficiency of the method is illustrated by numerical examples including a solid with single spherical cavity, solids with two interacting spherical cavities, and numerical homogenization of solids with cubic arrangement of spherical cavities. All results agree with analytical models available in the literature. The examples show that the method can be applied to the analysis of porous structures.

Wide-band slow light in compact photonic crystal coupled-cavity waveguides

Slow light has a variety of applications, in particular for enhanced nonlinear effects like four-wave mixing and high-harmonic generation. Here, we propose a photonic crystal coupled-cavity waveguide with an ultracompact arrangement of the constituent cavities in the propagation direction, and use an optimization algorithm to tune several structural parameters to engineer slow light with a constant group index ng over a wide bandwidth. We propose several specific silicon designs, including one with ng≈37 over a 20 nm wavelength range and another one with ng≈116 over an 8.8 nm band, which yields a group index–bandwidth product of 0.66—a record value among all slow-light devices. The design is experimentally beneficial because of its small footprint and straightforward fabrication and could find applications in optical storage or switching, and in generating quantum states of light.