Longitudinal Cavities Research Articles

Aerodynamic characteristics of axisymmetric boattail models with different number of longitudinal groove cavities

Reducing aerodynamic drag and increasing flying object performance is an important task in aerospace engineering. The high drag occurs for blunt base models, which are not only for missiles, and projectiles but also for building, bridges. This study presents numerical results regarding subsonic flow characteristics over axisymmetric boattail models equipped with longitudinal grooves, with the number of grooves ranging from 2 to 12. The standard model has a fixed boattail length of 0.7D and an angle 22°. The investigation employs numerical simulation methods utilizing the Reynolds-averaged Navier-Stokes (RANS) equations with the k-ω SST turbulent model. The boundary layer was captured well by the current simulation. The numerical results are initially validated against both simulated and experimental data from previous studies, ensuring accuracy and reliability. The findings indicate that an increase in the number of grooves from 0 to 4 results in a slight increment in drag. However, as the number of grooves is further increased from 6 to 12, a significant reduction in the model's drag is observed. Additionally, the flow patterns around the boattail model are visually depicted and analyzed to explain the drag trend of the model with different groove configurations

Two-component intra-cavity photoacoustic spectroscopy sensor using Y-shaped photoacoustic cell with two resonant cavities

In this paper, an intra-cavity photoacoustic spectroscopy (PAS) gas sensing system based on a 3D printed Y-shaped PAS cell with two longitudinal resonant cavities is designed for two-component detection. The sensor embeds the Y-shaped photoacoustic cell in the resonator of fiber ring laser for the intra-cavity gas detection, improving the laser power in the gas detection. The two resonant cavities of the Y-type PAS cell are formed into C-band and the L-band lasers, guaranteeing the laser stable output of C-band and the L-band. Comparing with the conventional dual-wavelength laser, the dual-wavelength laser scheme proposed in the paper eliminates the model competition and possesses much higher laser stability. A dedicated wavelength modulator is used to control the fiber bragger grating (FBG) to generate the stress change, and then scan the absorption peaks of the corresponding gases. The second harmonic (2f) PAS signal is used to calculate the gas concentration. The acetylene (C2H2) and carbon dioxide (CO2) were detected based on the frequency division multiplexing (FDM) technique using two resonant cavities. A microphone is used to simultaneously detect the photoacoustic signals of two resonance cavities. A demodulation frequency with a frequency intervals of 100 Hz ensures there is no cross-interference in demodulation of signals from each resonant cavity. The trace detection of C2H2 and CO2 was realized at normal temperature and pressure. The PAS signal intensity was further improved by optimizing the modulation amplitude and incident laser power. The minimum detection limits (MDLs) and the linear fit R-squared values (R2) of C2H2 and CO2 were 529 ppbv, 0.99971, 282 ppmv and 0.99991, respectively. It indicates that the two-component gas sensing system in this paper has good linearity and high sensitivity. It provides a valuable trace gas detection device for multi-component gas detection.

Flexural Behaviour of Hollow Reinforced Concrete T-Beams

Hollow reinforced concrete Tee beam (HRCTB) is a beam that has longitudinal cavities that can be made usually by placing recycled plastic pipes in the web of beam within the tension zone. These cavities are used to pass electrical and mechanical equipment as well as the economic and sustainable benefits coming from subtraction some amount of concrete from these beams. This study tries to investigate experimentally the effect of circular cavities depth and its geometrical shape on the flexural behaviour of hollow reinforced concrete Tee beams. The experimental program comprises constructing and testing seven reinforced concrete Tee beams that have total height of 300 mm, flange width of 250 mm, flange depth of 75 mm as well as web width of 150 mm with beam length of 2000 mm. The first specimen is solid specimen while the others are divided into two groups, the first group consists of three specimens that have different longitudinal cavities depth which are 105 mm, 170 mm and 235 mm measured from top fibre of beam, and the second group includes three specimens that have different geometrical shape which are sharp parabolic (diameters are 35 mm by 65 mm), normal parabolic (diameters are 40 mm by 60 mm) and circular cavity of 50 mm diameter respectively. The results showed that increasing cavities depth from 105 to 170 and 235 mm from the top fibre of beam reduced the relevant first crack load by 3.57 %, 7.14 % and 17.86 % respectively and reduced ultimate strength by 0.39 %, 1.03 %, and 2.31 % respectively. In addition, the results revealed that the first crack load decreased by 3.57 %, 7.14 % and 7.14 % and ultimate load strength decreased by 0.26 %, 0.39 % and 1.03 % respectively for sharp parabolic, normal parabolic and circular specimen respectively.

The role of the filamented multi-electron beams on electron azimuthal acceleration in a plasma waveguide

In this paper, a theoretical approach is presented for the electron azimuthal acceleration in a novel circular plasma waveguide. This special configuration includes a plasma column, whereas multiple parallel longitudinal cavities are located in it. Moreover, the plasma column surrounded by a dielectric tube, and the whole system is covered by a long cylindrical metallic waveguide. The location of each cavity in the plasma column is completely optional, and the electron beams with the different currents and velocities are injected inside them. By use of an accurate theoretical method, the field profile distribution is investigated. Besides, by applying boundary conditions, an expression for the general frequency spectrum of the surface azimuthal harmonics in the plasma waveguide is presented. The charged particle acceleration due to the tangential component of the electric field is investigated too. To investigate the effective factors on the azimuthal acceleration of the electrons, the configuration is specialized to a plasma waveguide containing two cavities.

Three-dimensional nonlinear finite element model to estimate backflow during flow-controlled infusions into the brain.

Convection-enhanced delivery is a technique to bypass the blood-brain barrier and deliver therapeutic drugs into the brain tissue. However, animal investigations and preliminary clinical trials have reported reduced efficacy to transport the infused drug in specific zones, attributed mainly to backflow, in which an annular gap is formed outside the catheter and the fluid preferentially flows toward the surface of the brain rather than through the tissue in front of the cannula tip. In this study, a three-dimensional human brain finite element model of backflow was developed to study the influence of anatomical structures during flow-controlled infusions. Predictions of backflow length were compared under the influence of ventricular pressure and the distance between the cannula and the ventricles. Simulations with zero relative ventricle pressure displayed similar backflow length predictions for larger cannula-ventricle distances. In addition, infusions near the ventricles revealed smaller backflow length and the liquid was observed to escape to the longitudinal fissure and ventricular cavities. Simulations with larger cannula-ventricle distances and nonzero relative ventricular pressure showed an increase of fluid flow through the tissue and away from the ventricles. These results reveal the importance of considering both the subject-specific anatomical details and the nonlinear effects in models focused on analyzing current and potential treatment options associated with convection-enhanced delivery optimization for future clinical trials.

Overview of Local Rod Defect Detection Studies

This article gives a review of three approaches to solving the problems of detecting local rod and pipeline defects and related problems. In the first approach, local defects are modeled by the matching conditions; in the second approach, by delta functions entering into the differential equation; and in the third approach, longitudinal cavities and cracks are modeled by continuous rod sections with modified stiffness, cross-sectional area, and density. This two-part review describes the works devoted to the detection of defects in distributed mechanical systems using natural frequencies, as well as using transmitted and reflected waves. The second part of the review is devoted to works that use the second and third approaches, i.e., defect modeling by delta functions and continuous rod sections with modified stiffness, cross-sectional area, and density.

Occurrence of Polymerization Shrinkage Stress and Observation of Longitudinal Sectioned Cavities in the Initial Curing Stage of Bulk-fill Resin Composite

Occurrence of Polymerization Shrinkage Stress and Observation of Longitudinal Sectioned Cavities in the Initial Curing Stage of Bulk-fill Resin Composite

Structural and electrical properties of geopolymer materials based on different precursors (kaolin, bentonite and diatomite)

Geopolymers (GP) were successfully synthesized from metabentonite (MB), metadiatomite (MD) and metakaolinite (MK). Characterization of their phase structure and microstructure was performed by XRD, FTIR, SEM/EDX methods. A SEM micrograph of GPMD shows a homogeneous surface with some longitudinal cavities in the gel, and it is significantly different from the micrographs of the other two geopolymer samples, GPMB and GPMK. A considerable amount of unreacted particles, as well as the presence of pores in the geopolymer matrix of GPMK and GPMD, indicate an incomplete reaction in the system. Aluminosilicate inorganic polymers, geopolymers, are quasi solid electrolytes which possess a high electrical conductivity at room temperature in relation to materials of similar chemical composition. The highest conductivity was found for the sample obtained from GPMK, amounting to 2.14 × 10–2 Ω–1cm–1at 700 ºC. The corresponding activation energies of conductivity for this sample amounted to 0.33 eV in the temperature range of 500–700 ºC. The geopolymer synthesized from metakaolin has good ionic conductivity values, which recommends it for use as an alternative material for an SOFC (Solid Oxide Fuel Cell).

Investigation of the second main problem of the theory of elasticity for a layer with several cylindrical cavities

Background. When designing spatial structures, parts and mechanisms, underground structures and communications, it is necessary to have an idea of the stress state of such a structure.Objective. It is necessary, with high accuracy, to find displacements and stresses in the body of the layer, which has longitudinal cylindrical cavities, and also to analyze its stress-strain state. At the boundaries of the layer and at the boundaries of the cavities, displacements are given.Methods. To achieve the declared goal, an analytical-numerical method has been developed for a layer with circular endless cylindrical cavities parallel to each other and to the surfaces of the layer. The solution of the spatial problem of the theory of elasticity is obtained by the generalized Fourier method with respect to the system of Lame equations in cylindrical coordinates associated with cylinders and Cartesian coordinates associated with layer boundaries. Special formulas are applied for the transition between coordinate systems for basic solutions. The infinite systems of linear algebraic equations obtained as a result of satisfying the boundary conditions are solved by the reduction method. A numerical study of the determinant gives reason to argue that this system of equations has a unique solution. As a result, displacements and stresses at various points of the elastic body of the layer were obtained. The reduction parameters were chosen so that the accuracy of the boundary conditions reached 10-4.Results. The analysis of the stress - strain state of the layer body at different geometric locations of two cylindrical cavities in it is carried out. It turned out that with equal distance between the cavity and the layer boundary from the surface of the cylinder in question, the layer boundary has a greater effect on the stress state of the body.Conclusions. With an increase in the reduction parameter, the accuracy of fulfilling the boundary conditions increases, but the calculation time also increases.The above analysis can be used for preliminary selection of the calculation model, and the proposed method for calculation, with high accuracy, the selected calculation scheme.

Three-dimensional envelope instability in periodic focusing channels

The space-charge driven envelope instability can be of great danger in high intensity accelerators and was studied using a two-dimensional (2D) envelope model and three-dimensional (3D) macroparticle simulations before. In this paper, we propose a three-dimensional envelope instability model to study the instability for a bunched beam in a periodic solenoid and radio-frequency (RF) focusing channel and a periodic quadrupole and RF focusing channel. This study shows that when the transverse zero current phase advance is below $90$ degrees, the beam envelope can still become unstable if the longitudinal zero current phase advance is beyond $90$ degrees. For the transverse zero current phase advance beyond $90$ degrees, the instability stopband width becomes larger with the increase of the longitudinal focusing strength and even shows different structure from the 2D case when the longitudinal zero current phase advance is beyond $90$ degrees. Breaking the symmetry of two longitudinal focusing RF cavities and the symmetry between the horizontal focusing and the vertical focusing in the transverse plane in the periodic quadrupole and RF channel makes the instability stopband broader. This suggests that a more symmetric accelerator lattice design might help reduce the range of the envelope instability in parameter space.

Absorption enhancement of thin film solar cells using back binary metallic grating

We reported in this work that light absorption can be significantly enhanced in an a-Si thin film solar cell with a nano binary metallic grating patterned on the bottom side. The enhancement is mainly due to combination of several kinds of optical modes. Cavity mode, at the transverse and longitudinal cavities and surface plasmon mode, propagating along the interface of silicon and silver are the main modes contributing to the enhancement. Some key parameters including grating period, width, height and active layer thickness are optimized. The integrated absorption rate of the optimized system reaches 76.55 % for the wavelength range from 300 to 950 nm under AM1.5G spectrum.

Broadband absorption and efficiency enhancement of an ultra-thin silicon solar cell with a plasmonic fractal

We report in this work that quantum efficiency can be significantly enhanced in an ultra-thin silicon solar cell coated by a fractal-like pattern of silver nano cuboids. When sunlight shines this solar cell, multiple antireflection bands are achieved mainly due to the self-similarity in the fractal-like structure. Actually, several kinds of optical modes exist in the structure. One is cavity modes, which come from Fabry-Perot resonances at the longitudinal and transverse cavities, respectively; the other is surface plasmon (SP) modes, which propagate along the silicon-silver interface. Due to the fact that several feature sizes distribute in a fractal-like structure, both low-index and high-index SP modes are simultaneously excited. As a whole effect, broadband absorption is achieved in this solar cell. Further by considering the ideal process that the lifetime of carriers is infinite and the recombination loss is ignored, we demonstrate that external quantum efficiency of the solar cell under this ideal condition is significantly enhanced. This theoretical finding contributes to high-performance plasmonic solar cells and can be applied to designing miniaturized compact photovoltaic devices.

Closure Behavior of Longitudinal Cavities in a Slab by Side Pressing

Longitudinal cavities or pipes are usually developed in a metallic slab or billet produced by continuous casting. In the present study, closure behavior of such cavities by side pressing was investigated by finite-element method. Since the contact surface between the dies and the slab was much longer in the longitudinal direction than in the thickness direction, the slab was compressed under the condition of plane-strain deformation. As a result, the effective strain was found to be an indicator for the void closure. The critical value of the effective strain was dependent upon the aspect ratio of the cross section of the cavity, but not upon its size.

The two-dimensional electroelasticity problems for multiconnected bodies situated under electric potential difference action

Solutions of the two-dimensional electroelasticity problems for infinitely long piezoelectric cylinders with cavities and cracks under electrical potential difference action are obtained using the Lekhnitskii’s generalized complex potentials. Herewith, piezoelectric bodies under consideration are free from mechanical loads, some (or all) openings and maybe the exterior boundary of the cylinders are fully covered by thin electrodes. Voltage differences are supplied on the electroded surfaces, the rest boundary surfaces are charge-free. In this case, the complex potentials are investigated. Boundary conditions are satisfied by the least-squares method. There are carried out numerical investigations of behaviour of some basic electroelastic characteristics in a circular hollow cylinder and in an infinite body with two longitudinal cavities and a charge-free plane crack. New electromechanical regularities of influence of material properties, geometrical characteristics of considered regions on values of electroelastic state characteristics and the stress, electric displacements and tensions intensity factor k1 are determined.

Erosion of carbon fiber composites under high-fluence heavy ion irradiation

The ion-induced erosion, determining by sputtering yield Y and surface evolution including structure and morphology changes of the modified surface layers, of two commercial carbon fiber composites (CFC) with different reinforcement – KUP-VM (1D) and Desna 4 (4D) have been studied under 30 keV Ar + high fluence ( φt ∼ 10 18–10 20 ion/cm 2) irradiation in the temperature range from room temperature to 400 °C. Ion-induced erosion results in the changes of carbon fiber structure which depend on temperature and ion fluence. Monitoring of ion-induced structural changes using the temperature dependence of ion-induced electron emission yield has shown that for Desna 4 and KUP-VM at dynamic annealing temperature Т а ≈ 170 °С the transition takes place from disordering at T < T a to recrystallization at T > T a. The annealing temperature Т а is close to the one for polycrystalline graphites. Microscopy analysis has shown that at temperatures Т < T a the etching of the fibers results in a formation of trough-like longitudinal cavities and hillocks. Irradiation at temperatures T > T a leads to a crimped structure with the ribs perpendicular to fiber axis. After further sputtering of the crimps the fiber morphology is transformed to an isotropic globular structure. As a result the sputtering yield decreases for Desna 4 more than twice. This value is almost equal to that for KUP-VM, Desna 4, polycrystalline graphites and glassy carbons at room temperature.

Designing old forest for the future: Old trees as habitat for birds in forests of Mountain Ash Eucalyptus regnans

Old trees are one of many habitat attributes associated with old forests. They are known to be required by many wildlife species including cavity-dependent birds. Forest managers need to select strategies for retaining and regrowing old trees to maintain suitable numbers over time at appropriate configurations in the forest landscape. This paper presents data from wet forests in south-eastern Australia to help elucidate the effects of different strategies on forest birds as one element of biodiversity that needs to be conserved in these forests. Bird abundance was assessed by standard area search at 117 sites in forests of Mountain Ash Eucalyptus regnans in the Victorian Central Highlands, over the course of two spring-summer breeding seasons from 1996 to 1998. The sites contained 60-year regrowth from extensive wildfires in 1939, along with varying numbers of older trees that had survived the fire. Some of the old trees were dead and at varying stages of decay. Numbers of old trees were counted at each site and a range of other habitat measurements taken. Birds were considered by species or guilds of species (feeding and nesting guilds). Bird abundance data were regressed against numbers of old trees and other relevant habitat data. Cavity-nesting birds were positively related to numbers of old trees, and especially to those that remained alive. Bird species that nest in longitudinal cavities in small branches (spouts) were rare at sites that lacked old trees, and were related strongly to numbers of live old trees. Large cavity-nesters were related to numbers of live old trees or all old trees. Treecreepers correlated less strongly, perhaps because they use cavities in decaying snags and stumps as well as large old trees. Honeyeaters and Mistletoe birds were also positively associated with numbers of live old trees, although they do not need cavities. Total bird abundance was positively related to live, dead or all old trees. Several other relationships were found. For example, shrub foragers were related positively to abundance of tall shrubs but not low shrubs; wattle foragers were related positively to abundance of wattles (especially Silver Wattles Acacia dealbata); and Eastern Spinebills Acanthorhynchus tenuirostris were positively associated with abundance of Mountain Correa Correa lawrenciana (the flowers of which provide a major source of nectar). Non-linear relationships between bird abundance and densities of old trees were found for at least two cavity-nesting bird species. The relationship was convex for Striated Pardalote Pardalotus striatus (optimum density 5–12 live old trees/ha) and mildly concave for Crimson Rosella Platycercus elegans. This suggests that the former would benefit from strategies to disperse old trees among regrowth at suitable scales whereas the latter would benefit from strategies to produce clumped distributions of old trees. However, Striated Pardalotes showed a strong preference for live old trees, which cannot easily be kept alive among regrowth after logging or fire, suggesting clumped retention may be more practical for that species too. Three other species showed weak evidence of non-linear responses, but most species showed no significant evidence of departure from linearity. No species or guild showed strong evidence of a threshold level of old tree density (above ∼1 ha −1) below which those birds would not occur. Hence for most of the diurnal birds considered in this study, old trees appear to be useful in proportion to the overall number of suitable old trees that can be retained and regrown (rather than their spatial pattern), and especially the number that can be kept alive. Clumped retention strategies give the best chance of keeping many retained trees alive in retained patches. Otherwise, spacing patterns should be a secondary consideration, except where they are known to be important for species such as owls and arboreal mammals.

Histological examination of the chaetognathan morphological structure in the region of a supposed trunk-tail septum

A histological examination was conducted based on sections done in series in transverse and longitudinal directions of Aidanosagitta macilenta (Sagittidae, Chaetognatha) in a region which includes the anterior parts of the testes and the posterior part of the ovaries. We found that, in mature individuals (the 4th stage of maturation), the anterior parts of the testes are located in front of the posterior part of the ovaries. The anterior parts of the testes have a ventral position adjoining the ventral muscular bands. The ovaries are located more dorsally than the testes at the level of lateral fi elds. A transverse trunk-tail septum between testes and ovaries was not revealed. These data support an idea that a structure which was earlier treated as a tail-trunk septum is actually the anterior edges of the testes. Both longitudinal coelomic cavities continue into the tail region without any transverse septa. The paired tail cavities as can be seen from their composition and functions represent the testes consisting of a peripheral compact portion with undifferentiated germ cells and a space where the maturation of cells occurs. The tail is distinguished anatomically as a post-anal portion of the body but it is not a true segment as it is not separated from a trunk part of the body by the trunk-tail septum. The body of Chaetognatha consists of two true parts (segments). A mesenterial septum divides the body longitudinally-symmetrically from a trunk-head septum down only to the caudal end of the gut. In the tail region there is a medial septum formed by the medial walls of testes. Gonads in both females and males do not have any duct connecting them with a gut cavity. The ovaries and the testes are covered by a coelomic lining and a duct between the ovaries and the testes is absent.

Cavity-QED-based entangled photon pair gun

We describe a cavity-QED scheme to deterministically generate polarization entangled photon pairs by using a single atom successively coupled to two single longitudinal mode cavities presenting polarization degeneracy. The cavities are initially prepared either in the vacuum state or in a single photon Fock state for each orthogonal polarization. Sharing the same basic elements, the source can operate on different physical processes. For a V-type three-level atom initially prepared in the ground state two implementations of the source are possible using either: i) two truncated Rabi Oscillations, or ii) a counterintuitive Stimulated Raman Adiabatic Passage process. Although slower than the former implementation, this second one is very efficient and robust under fluctuations of the experimental parameters and, particularly interesting, almost insensitive to atomic decay. For a four-level atom in a diamond configuration initially prepared in the upper state, the source can produce entangled photon pairs even in the bad cavity limit via an adiabatic passage process. We have performed Monte Carlo wave function simulations to characterize these sources by means of: i) the success probability P of producing the desired entangled state, ii) the fidelity F in the reduced space of two emitted cavity photons, and iii) the S parameter of the Clauser-Horne-Shimony-Holt (CHSH) inequality to quantify the entanglement capability.

Cavity-quantum-electrodynamics entangled photon source based on two truncated Rabi oscillations

We discuss a cavity-QED scheme to deterministically generate entangled photons pairs by using a three-level atom successively coupled to two single longitudinal mode high-Q cavities presenting polarization degeneracy. The first cavity is prepared in a well defined Fock state with two photons with opposite circular polarizations while the second cavity remains in the vacuum state. A half-of-a-resonant Rabi oscillation in each cavity transfers one photon from the first to the second cavity, leaving the photons entangled in their polarization degree of freedom. The feasibility of this implementation and some practical considerations are discussed for both, microwave and optical regimes. In particular, Monte Carlo wave function simulations have been performed with state-of-the-art parameter values to evaluate the success probability of the cavity-QED source in producing entangled photon pairs as well as its entanglement capability.

Pressure wave propagation in fluid-filled co-axial elastic tubes. Part 1: Basic theory.

Our work is motivated by ideas about the pathogenesis of syringomyelia. This is a serious disease characterized by the appearance of longitudinal cavities within the spinal cord. Its causes are unknown, but pressure propagation is probably implicated. We have developed an inviscid theory for the propagation of pressure waves in co-axial, fluid-filled, elastic tubes. This is intended as a simple model of the intraspinal cerebrospinal-fluid system. Our approach is based on the classic theory for the propagation of longitudinal waves in single, fluid-filled, elastic tubes. We show that for small-amplitude waves the governing equations reduce to the classic wave equation. The wave speed is found to be a strong function of the ratio of the tubes' cross-sectional areas. It is found that the leading edge of a transmural pressure pulse tends to generate compressive waves with converging wave fronts. Consequently, the leading edge of the pressure pulse steepens to form a shock-like elastic jump. A weakly nonlinear theory is developed for such an elastic jump.