Cavity Height Research Articles

Quarter Wavelength Fabry–Perot Cavity Antenna with Wideband Low Monostatic Radar Cross Section and Off-Broadside Peak Radiation

Since antennas are strong radar targets, their radar cross section (RCS) reduction and radiation enhancement is of utmost necessity, particularly for stealth platforms. This work proposes the design of a Fabry–Perot Cavity (FPC) antenna which has wideband low monostatic RCS. While in the transmission mode, not only is gain enhancement achieved, but radiation beam is also deflected in the elevation plane. Moreover, the design is low-profile, i.e., the cavity height is ~λ/4. A patch antenna designed at 6 GHz serves as the excitation source of the cavity constructed between the metallic ground plane and superstrate. The superstrate structure is formed with absorptive frequency selective surface (AFSS) in conjunction with dual-sided partially reflective surface (PRS). Resistor loaded metallic rings serve as the AFSS, while PRS is constructed from inductive gradated mesh structure on one side to realize phase gradient for beam deflection; the other side has fixed capacitive elements. Results show that wideband RCS reduction was achieved from 4–16 GHz, with average RCS reduction of about 8.5 dB over the reference patch antenna. Off-broadside peak radiation at −38° was achieved, with gain approaching ~9.4 dB. Simulation and measurement results are presented.

Unidirectional switching of magnetic vortex core in a nanocavity mediated nanodisk: Looking for a reliable low-power-driven and fast switching in terms of geometric parameters

Reliable unidirectional switching of magnetic vortex core driven by continuous rotating magnetic field is investigated using a permalloy nanodisk with a nanocavity inserted in the center in combination with micromagnetic simulations. It is reported that once the vortex core is confined in a nanocavity of diameter is comparable to the core size, the modes of the core motion (divergence/convergence modes) are modulated differently by the nanocavity: the threshold field amplitude required for vortex core switching is reduced for convergence mode, but not for divergence mode. We found that the confinement of the nanocavity to the core is mediated by the cavity height as well. Low-power-driven fast unidirectional switching is found to be achievable by carefully choosing the value of the nanocavity height.

Tubular reactor internals for suppressing hot spot formation applied to the Fischer-Tropsch reaction

A tubular reactor internals was proposed in order to suppress hot spot formation in catalyst bed. The reactor internals was designed to adjust the effective inner diameter in the front region of the catalyst bed where the hot spot was most likely to be formed. A bench-scale CFD reactor model with a 50 mm diameter and 1000 mm height was employed to verify the performance of the reactor internals under Fischer-Tropsch reaction conditions and to optimize its key parameters: neck diameter and frustum cavity height. The simulation results for the optimized reactor internals showed that the maximum temperature rise decreased by as much as 22.6 % while the change in the rate of CO conversion was less than 2.13 % and the C3+ product selectivity increased slightly.Moreover, the mechanism whereby the internals inhibiting the hot spot was discussed from the aspects of the heat transfer and the dispersion of reaction heat intensity.

A thermal-driven method based on Brillouin fiber-optic sensors for the quantitative identification of subsurface cavities in concrete-filled steel tube structures

In the composite structure of a concrete-filled steel tube (CFST), because the concrete is concealed inside the steel tube, subsurface cavities can occur and are difficult to identify. In this study, a thermal-driven method based on Brillouin fiber-optic sensors (BFOSs) was proposed to quantitatively identify subsurface cavities in CFSTs. By performing a thermodynamic analysis of subsurface cavities in CFSTs, a thermal model related to the relationship between the subsurface cavity size and the temperature rise at the top surface of the CFST was established for the first time. Then, a sensing scheme based on the BFOS was proposed, and its feasibility was evaluated through an experimental program. The experimental program involved the use of an active heating layer for inputting heat flow into the CFST structure and BFOSs for the distributed measurement of temperature to identify subsurface cavities in CFSTs. The experimental results indicated that the BFOSs can achieve real-time distributed measurements of the surface temperature of the CFSTs. According to the temperature anomalies in the temperature rise curves of the CFSTs, the subsurface cavities can be accurately located in the longitudinal direction of the CFST, and its length can be quantified. There is an obvious linear relationship between the temperature rise and the square root of the heating time, from which the equivalent heat absorption coefficient (EHAC) can be determined. Furthermore, according to the relationship between the subsurface cavity height and the EHAC in the thermodynamic theoretical analysis, the subsurface cavity height can be obtained quantitatively.

The Coronal Pulp Cavity Index an aid in age determination -A Cone Beam Computed Tomography Study

Background: The objective of the present study was to assess the accuracy of age estimation from TCI ofmandibular molars (except wisdom teeth) of both sides using CBCT images of known age and sex, so thatwe can apply this method to estimate age in both living individuals and skeletal material of unknown age.Methods: A cross sectional retrospective study was conducted on a total of 100 CBCT images of subjectswho were referred to the department for varied diagnostic purposes of known age and gender. All CBCTimages with a fully visible pulp cavity were selected. Two measurements were taken at two different levels.Height of the crown (CH) and height of the coronal pulp cavity (CPCH). Then tooth – coronal index (TCI)for each tooth was calculated as follows: TCI = CPCH X 100 / CH.Results: Comparison of TCI value between male and female showed no significant difference between thegender. Among the four mandibular molars (lower left and right1stand 2nd molars) 46 and 47 TCI correlateswell with age. TCI of 46 has significant prediction of age in female with an R value of 0.426. Inter observermeasurements showed a moderate to good agreement of the measures.Conclusions: TCI method of mandibular teeth was found to be a reliable method for age estimation and notgender determination. CBCT can be used in age determination for forensic purposes as it is non- invasiveand also makes it possible to reconstruct the images in different planes showing the anatomical and imagedstructures at different planes.

Fabry-Perot Antenna Employing Artificial Magnetic Conductors and Phase Gradient Metasurface for Wideband Monostatic RCS Reduction and High Gain Tilted Beam Radiation

Platforms with low radar signatures require compatible antennas (low scattering) for communication purposes. Under this context, the article presents two Fabry-Perot (FP) Cavity antennas (Ant-1 and Ant-2). Ant-1’s aperture is an integrated design of artificial magnetic conductor (AMC) surface and a phase gradient metasurface (PGM), incorporating three unit-cell structures. The antenna achieves reduced monostatic scattering over broad bandwidth, and simultaneously obtains high gain as well as tilted beam peak radiation. Patch radiating at 7 GHz forms excitation source of the cavity, and cavity height is $0.33\lambda $ , smaller than the heights of conventional cavity designs ( $\lambda $ /2). RCS reduction is obtained over a bandwidth of 105.8% (4-13 GHz) for arbitrary polarizations, covering C/X bands. Antenna gain is 12 dB, and peak radiation tilt is −60° in elevation plane. Simulations have been verified through fabricated prototype. Ant-2 is a modification of Ant-1. Ant-2’s aperture is constructed from two unit-cell structures, and its aperture size is 41% smaller than Ant-1. Its cavity height is $0.3\lambda $ . Ant-2 also achieves wideband backscattering reduction; however, due to asymmetric layout of unit-cell elements over the aperture, radar cross section (RCS) reduction bandwidth is different for the two polarizations. For vertically polarized (VP) incident wave, RCS reduction bandwidth is 105.8% (4-13 GHz), but for horizontally polarized (HP) wave, it is 85.7% (5.2-13 GHz). Nevertheless, broadband RCS reduction is still achieved for both polarizations. Peak gain is 11.73 dB, achieved at −37° tilt angle. Simulations are presented for Ant-2. Compared to literature, both antennas show various improved results.

Folding photopolymerized origami sheets by post-curing

The paper presents a novel manufacturing approach to fabricate origami based on 3D printing utilizing digital light processing. Specifically, we propose to leave part of the model uncured during the printing step, and then cure it in the post-processing step to set the shape in a folded configuration. While the cured regions in the first step try to regain their unfolded shape, the regions cured in the second step attempt to keep their folded shape. As a result, the final shape is obtained when both regions’ stresses reach equilibrium. Finite element analysis is performed in ANSYS to obtain the stress distribution on common hinge designs, demonstrating that the square-hinge has a lower maximum principal stress than elliptical and triangle hinges. Based on the square-hinge and rectangular cavity, two variables—the hinge width and the cavity height—are selected as principal variables to construct an empirical model with the final folding angle. In the end, experimental verification shows that the developed method is valid and reliable to realize the proposed deformation and 3D development of 2D hinges.

Tooth Coronal Index: A Novel Tool For Age Estimation on Cone-Beam Computed Tomography

Objective: To evaluate dental age assessment reliability through Tooth Coronal Index (TCI) method. Material and Methods: The cone-beam computed tomography (CBCT) scans of 160 individuals aged between 20-70 years were analyzed in the present study. The height of the crown, i.e., coronal height, and the height of the coronal pulp cavity, i.e., coronal pulp cavity height, of mandibular second premolars and first molars were calculated and then TCI was measured. The actual age of a subject was compared with TCI of tooth and the acquired data were subjected to Pearson’s correlation and unpaired t-tests. Results: Negative correlation was observed between the real age and TCI of mandibular first molar (r = -0.094, p=0.382) and second premolar (r = -0.176, p=0.0961. Statistically significant difference was observed between actual age and TCI for mandibular second premolar and first molar (p<0.001). Conclusion: Tooth coronal index has the potential to estimate age of an individual on CBCT scans. It is simple, cost-effective than histological methods and can be applied to both living and unknown dead.

Anatomometric characteristics and pleural cavity changes after pneumonectomy

To analyze the anatomometric characteristics of post-pneumonectomy cavity and their changes at various times after surgery. The study included 47 patients aged 39-75 years after pneumonectomy (right-sided - 23 cases, left-sided - 24 cases). Computed tomography was performed prior to surgery, in 10-12 days, 6 and 12 months after intervention. Transverse, anteroposterior dimensions, height and volume of pleural cavity were evaluated using CT scans and 3D models. Post-pneumonectomy cavity decreases and changes own shape in postoperative period. Reduction is mainly caused by decrease in its height. The volume of post-pneumonectomy cavity was decreased in early postoperative period by 1.8 times compared to preoperative values (from 3351.5±150.0 cm3 to 2112.1±152.6 cm3 on the right side and from 2674.3±125.2 cm3 to 1460.1±84.1 cm3 on the left side). After 12 months, this value was reduced by 3.68 times compared to early postoperative period (714.3±100.7 cm3 on the right and 401.5±42.5 cm3 on the left). The shape changes consist of flattening and sinus depth reduction. Exudate density was similar throughout a year. The capsule was formed in 74.1% of patients after 12 months. There was no correlation between the cavity reduction and patient constitution. Post-pneumonectomy cavity is a dynamically changing anatomical formation participating in the mechanisms of compensation for changes after pneumonectomy. The most significant collapse of post-pneumonectomy cavity occurs in early postoperative period. Cavity reduction degree does not depend on individual characteristics of patients.

Sensitivity Analysis on Dielectric Modulated Ge-Source DMDG TFET Based Label-Free Biosensor

This work compares the performance of dielectric modulated (DM) based Ge-source dual material double gate (DMDG) Tunnel Field Effect Transistor (TFET) and conventional (C)-DMDG-TFET as label free biosensor through Technology Computer Aided Design (TCAD) simulator. Here, cavity is introduced both at source and drain sides of the fixed HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> dielectric to increase the capture area of biosensors. Sensitivity (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> ) is extracted for both neutral and charged (positive/negative) biomolecules considering cavity is fully filled with different dielectric materials (k). We have reported the sensitivity with the variation in height of nanogap cavity (h <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bio</sub> ) for neutral biomolecules in the cavity. The sensitivity of Ge-source DMDG-TFET is found higher than C-DMDG-TFET due to more conduction at the tunnel junction. Also, the subthreshold swing (SS), transfer characteristics, and I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> ratio of these biosensors are reported for different k and h <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bio</sub> considering neutral/charged biomolecules. The sensitivity of partially filled nanogaps with biomolecules like decreasing, increasing, concave, and convex step profiles are reported for both the biosensors. The dynamic range (DR) of both the biosensors are extracted in presence of positive and negative charged biomolecules. The response time of Ge-source DMDG-TFET is reported at different k. A comparative study of proposed biosensor with other reported work is discussed. Finally, the sensitivity is extracted for DMDG-TFET considering other source material like GaAs, InAs, Si-Ge hetero stacked (HS), GaAs-InAs HS.

PIV study of directional solidification of a binary metal alloy analogue

Flows driven by double-diffusive convection during alloy solidification strongly influence the macroscopic solute redistribution, localized remelting and solidification rates which play a dominant role in determining the mechanical, electrical and thermal properties of the final product. This experimental study is carried out to investigate the effect of initial concentration and initial cavity height on the development of double-diffusive convection and on the real-time solidification interface growth during solidification of aqueous sodium chloride solution in a top-cooled rectangular cavity. Aqueous sodium chloride solution is widely used as an analogues model system for most of the alloys to study their solidification behaviour because of its transparency that enables the flow visualization using optical techniques. In the present work, particle image velocimetry (PIV) method is used for the velocity measurement during solidification. PIV measurements show that on increasing the initial concentration and the initial cavity height, the strength of the convection flow increases. The evolution of solidification is also captured using a high-speed (HS) camera. The images captured during solidification indicates that the wavy interface formed due to remelting phenomena caused by double-diffusive convection. Further, we also noticed that the solidification rate decreases by increasing the initial concentration and decreasing the initial cavity height.

Evaluation of Successful and Failed Filtering Blebs after Trabeculectomy Using Anterior Segment Optical Coherence Tomography.

Purpose:To evaluate filtering bleb characteristics using anterior segment optical coherence tomography (AS-OCT) and analyze correlations between these parameters and intraocular pressure (IOP).Methods:The study included 54 eyes of 43 patients who underwent trabeculectomy with mitomycin-C. The patients were divided into two groups based on mean postoperative IOP. The criterion for surgical success was mean unmedicated postoperative IOP ≤18 mmHg. Patients with IOP values >18 mmHg were prescribed anti-glaucoma drops and classified as a surgical failure. All patients underwent AS-OCT, and maximum bleb height, maximum bleb wall thickness, and maximum fluid-filled cavity height were measured. AS-OCT bleb parameters were compared between the successful and failed groups.Results:Of the 54 eyes, 37 (68.5%) were in the successful group, and 17 (31.5%) were in the failed group. Mean preoperative IOP values in the successful and failed groups were 26.9 ± 6.5 mmHg and 22.9 ± 4.9 mmHg, preoperatively, versus postoperative values of 13.3 ± 2.1 mmHg and 22.8 ± 2.8 mmHg, respectively. Mean postoperative follow-up time was 17.4 ± 9.5 months in the successful group and 19.1 ± 10.1 months in the failed group (P = 0.22). In the successful and failed groups, mean bleb height was 1473.7 ± 150.6 μm and 1165.4 ± 217 μm (P < 0.001), bleb wall thickness was 670.5 ± 119.9 μm and 538.8 ± 144.3 μm (P = 0.001), and fluid-filled cavity height was 736.5 ± 196.8 μm versus 532.5 ± 226.2 μm (P = 0.001), respectively.Conclusions:The results of this study showed that higher AS-OCT values for bleb height, wall thickness, and fluid-filled cavity height were associated with greater functional success. These parameters may be helpful in determining bleb functionality.

Temperature stability study of resonant angular scanning micromirrors with electrostatic comb-drive actuators

Resonant rotational scanning micromirrors with electrostatic comb-drive actuators are widely used in generating structured lights for 3D sensing, but their resonant scanning stability is affected considerably by the working temperature, which in turn compromises the sensing accuracy. The resonant scanning instability is mainly exhibited as the temperature drifts of the quality factor (Q) and the resonance frequency. In this paper, we focus on the Q variation due to the temperature dependence of air damping. The temperature dependence of the air damping in a comb-drive micromirror is investigated using both simplified analytical damping models and computational fluidic dynamic (CFD) models. The modeling results show that the temperature dependence of the viscous damping of the comb drive is opposite to that of the drag damping of the mirror plate, providing a means of minimizing the temperature dependence of Q by adjusting the structural parameters of the comb drive and the mirror plate. It has also been found from the modeling that the lengths of the comb-drive fingers and the mirror plate play the most significant role while the cavity height under the mirror plate has little effect if it is more than 10 % of the mirror plate length. Meanwhile, four micromirrors with different comb-finger or mirror-plate lengths are designed and fabricated. The testing results from these four fabricated mirrors have confirmed that the temperature coefficient of the Q value of an angular scanning comb-drive micromirror can be altered and ultimately compensated by changing the mirror-plate and/or comb-finger lengths.

Configuration and impurity quantification of AmLi sources using radiography and gamma spectroscopy

This paper presents the non-destructive assay of two AmLi sources used for detector characterization and active interrogation at PNNL, identified as MRC-101 and MRC-103. First, a detailed description of the internal configuration of 2724-BT encapsulated MRC sources is established. X-ray radiographs of the AmLi sources are reported for the first time to verify the dimensions and orientation of the encapsulation. Notably, a density variation was observed as a contrast change across the height of the source cavities. Contrary to commonly made assumptions in literature, it is indirectly observed that the AmLi source/target material only occupies a portion of the source cavity. The intensity of the prompt gamma-rays resulting from the inelastic scatter of alpha particles on 7Li was used to calculate the mass ratios of LiH:AmO2. The gamma-ray spectra revealed the presence of numerous impurities in both source and target material (243Am, 237Np, 154Eu, 23Na, and 9Be). Neutron-gamma production ratios were applied to the intensity of the Doppler-broadened peaks from alpha-induced reactions with 7Li, 9Be, and 23Na to calculate neutron rates for both sources. A neutron/alpha production yield (derived in this work) was then related to the atomic concentration of these isotopes to find the approximate masses within each source. Ultimately, the AmLi source density was estimated with prompt gamma analysis based on partial source volumes as 0.45±0.08g∕cm3.

Anatomycal features of the ethmoidal labyrinth and nasal cavity structures in childhood

The morphotopometric variability of the ethmoidal labyrinth and the parameters of the nasal cavity for 87 childrens cranium (121 years) has been determined. The growth of the ethmoidal labyrinth and the nasal cavity occurs undulating and unevenly. The increase of the height of the ethmoidal labyrinth begins earlier than its width and length from 23 years to 1316 years old. Growth periods the height of ethmoidal labyrinth occur for 23 years, 812 and 1316 years; widths 47, 812 and 1721 years; length 47, 812 and 1316 years. At the ethmoidotomy in the infant and early childhood, the smallest size of the ethmoidal labyrinth should be taken into account: width 78 mm, height 1416 mm, length 2729 mm, so in these age periods there is a high risk of damage of the cribriform and orbital plates ethmoid bone with the development of iatrogenic complications. The nasal cavity штchildren expands posteriorly as well as in adults. In the infancy, the width of the nasal cavity at the back corresponds to the width in the front section, from 2 years prevails than in front and by adolescence becomes larger for 33,5 mm. Knowing these agerelated features of the structure of the childrens nasal cavity, during surgery the rhinosurgeon when shifting the middle nasal shells medially or laterally should ensure to maintain the physiological model of the nasal cavity. In infancy, the width of the ethmoidal labyrinth is larger than the width of the nasal cavity by 38,5%, and by adolescence this ratio increases to 76,8%. The length of the nasal cavity increases from 47 years to adolescence, the length of the ethmoidal labyrinth grows parallel to the maximum length of the nasal cavity and it is less for more than a half in all childrens age groups: in the infancy by 74%, in adolescence by 85.1%. The height of the nasal cavity is twice the height of the labyrinth in any childhood age, the distance from the bottom of the nasal cavity to the lower edge of the middle nasal shell must be correlated with the distance above the level of the average nasal shell during intranasal surgeries and do not exceed it for the introduction of tools.

Attributes of Eurasian Green Woodpecker (Picus viridis) nest cavities in Hungary

Abstract Thirty-three nest cavities of Green Woodpeckers (Picus viridis) in Hungary were documented over a period of 15 years (2006–2020). Thirteen different tree species were used. All documented cavities were in the main trunks of trees. The mean cavity height was 5.6 m and 1.5 m standard deviation and ranged from 2 to 9 m. Tree trunk diameters ranged between 36–55 cm with a mean of 43.1 cm and 4.2 cm standard deviation. A southerly orientation of cavity entrances prevailed with a mean direction of 187° clockwise from north. The results suggest that cavity-entrance orientation was non-random.

Numerical analysis of the flow-induced vibrations in the laminar wake behind a blunt body with rear flexible cavities

We present a numerical study on the fluid–structure interaction of an incompressible laminar flow around a slender blunt-based body implementing a rear cavity of flexible plates. The study focuses on the use of this type of device to control the wake dynamics and the aerodynamic forces acting on the body, as well as to harvest energy from the flow. To that aim, the effects on the plates flow-induced vibrations (FIV) and on the dynamics of the flow of three control parameters, namely the reduced velocity, 0≤U∗<12, the mass ratio, m∗=[500,1000] and the cavity height hc, are evaluated at Reynolds number Re=500. Four different branches are identified in terms of dynamic response, as U∗ increases, regardless of the values of hc and m∗. At low values of U∗, an initial branch with a local peak of moderate amplitude response is observed, where the plates oscillate in counter-phase, in a varicose mode, with a frequency fp that is synchronized with the second harmonic of the vortex shedding frequency, 2fvs, and similar to the natural frequency of the solid, fn≃f1,n. For intermediate values of U∗, a transition towards a sinuous mode of oscillation occurs, where the plate frequency is synchronized with the vortex shedding frequency, fp=fvs. Initially, after such transition, the oscillation frequency is lower than the natural frequency of the plates fp<f1,n, so that a weak response defines a lower branch in the amplitude response curve. When U∗ increases, a lock-in regime develops with fp=fvs=f1,n, that is characterized by a response amplification, giving rise to the emergence of the upper branch, where the FIV amplitude of plates is the highest. Finally, a fourth desynchronization branch of moderate amplitude appears for larger values of U∗, where the plates present a complex, multi-mode regime, characterized by the vibration at multiple frequencies within the range 5f1,n<fp<6.5f1,n. The analysis of the plates deformation through POD analysis reveals that they mainly oscillate following the first Euler–Bernoulli mode for the first three branches, and a combination of the second and first Euler–Bernoulli modes for the desynchronization branch. The effect of increasing the mass ratio is to mitigate the response at higher values of U∗, while reducing the cavity height hc leads to the fostering of oscillations within the upper and desynchronization branches. In general, the FIV response of plates alters the wake dynamics and the force coefficient, especially within the lock-in regime, where the drag is strongly amplified, although the fluctuations of the lift are attenuated (nearly a 40% reduction). Besides, reductions of the drag of approximately 2% are obtained within the initial and lower branches. Finally, a simple quantification of the energy transfer from the plates, through a linearized Euler–Bernoulli approach, shows that the lock-in regime represents the best regime to extract energy from the flow.

Age-related description of the posterior structures of the nasal cavity in children

The aim of the study was to describe morphometric characteristics of the posterior parts of the nasal cavity in different periods of childhood and to specify the age-related norm for improving surgical treatment options of choanal atresia and providing an optimal access to the anterior part of the skull base. Material and methods. The study included 87 children aged 1-21 who were exposed to craniometry of the nasal cavity structures. Results. The age-related variability of the linear dimensions and shape of the choanae, their relationship with the dimensions of the pyriform aperture and the height of the nasal cavity in the posterior part were defined in the study. The increase in the height of the choanae and the height of the nasal cavity at the back starts from 2– 3 years of age, and the width – from 8–12 years of age. The height and width of the pyriform aperture are equal to the age of 8–12; these parameters increase in older children's groups with a predominance of the height over the width. The height of the nasal cavity at the back increases in all age periods. The growth of the studied structures of the nasal cavity is completed by adolescence. In infancy, the height of the choanae is less than the height of the nasal cavity at the back by 45%, and less than the height of the pyriform aperture by 20%; in adolescence, these ratios are 42% and 23%, respectively. In infancy the choanal width is less than the width of the pyriform aperture by 49%, and in adolescence – by 40%. In infancy and early childhood, the choanae are typically small in height and width. Their shape is round in 25% of cases, however, ovoid shape is also found. The height and width of the pyriform-shaped aperture at these age periods are similar and do not exceed 17–18 mm; the height of the nasal cavity at the back is 25–27 mm. Conclusion. The authors have described age-related morphometric features of the posterior structures of the nasal cavity. These features should be taken into account by otorhinolaryngologists and neurosurgeons when planning endoscopic intranasal surgical access in children. The younger the child is, the more difficult it is to perform a surgery due to the significant restriction of the access resulted from the small size of the piriform opening and the nasal cavity, and the obstinacy of the nasal septum. When performing choanotomy for atresia, it is necessary to form the choana comparing it in shape and size with the age-related norm

Acoustic radiation force and torque on spheroids inside an ideal cylindrical cavity

We perform a theoretical analysis of the radiation forces and torques produced on a spheroid particle by the acoustic modes of an ideal (with a rigid top and bottom and with soft or hard lateral walls) cylindrical chamber. Exact analytical expressions are obtained for a rigid particle and assuming the fluid inviscid approximation. A particular emphasis is given to the resonator's fundamental mode for which the axial and radial trap stiffnesses are calculated. The axial trap stiffness depends inversely with the cavity's height squared. We also predict that the radiation torque induces the particle to oscillate around its minor axis. The corresponding oscillation frequency is then determined. The theory is showcased for studying the dynamics of an Au microrod (modeled as an elongated spheroid) with a 20 μm-length and 2 μm-width in a water medium. In doing so, we use typical parameters of acoustofluidic devices (cavity's dimensions and energy density). The obtained results show terminal velocities of few micrometers per second, while the oscillation frequency is in the kilohertz range. In addition, a discussion on the dynamics of micro-/nanorobots of spheroidal shape propelled by ultrasound is outlined.

Experimental Investigation on the Vapor Chambers with Sintered Copper Powder Wick

High power electronics units generate high-density heat flux, which poses a significant threat to the reliability of these devices. The vapor chamber (VC) has a very high heat transfer rate and has a wide range of applications in the heat dissipation of electronic products. VCs with sintered copper powder wicks sized as irregular shape copper powder 50 µm (I-50 µm), I-75 µm, I-110 um, I-150 µm were studied in this paper. The effect of liquid filling ratio was discussed. The results indicated that the thermal resistance of all VCs decreased with the increase of heating power. The capillary performance of wick was the dominant factor for the heat transfer performance of VCs with different kinds of wick. A capillary performance factor was proposed to evaluate the capillary performance of VCs. The capillary performance factor of VC with the wick of I-75 µm was much higher than that of the other types of VC in this study. The heat source surface temperature of VCs could be affected by filling ratio and wick structure. But, it should be insensitive to the filling ratio when a better capillary performance factor was obtained. With the same heating area and similar structure, the maximum heat flux density of the VC would decrease as the height of vapor cavity decreased.