Cavity Depth Research Articles

Coupling parameter analysis of photovoltaic double skin façade targeting photovoltaic etching ratio and cavity depth

The photovoltaic double skin façade (PV-DSF) represents the frontier of the advanced building envelope, whereas the prior parameter analysis had predominantly focused on the influence of individual factors. As two essential factors of PV-DSF, the photovoltaic etching ratio ϑ and cavity depth Dcav have garnered considerable academic attention, with little of them focusing on their coupling effect to energy performance. This paper investigates the impact of ϑ and Dcav using a spectrum-resolution numerical model, incorporating the concept of elementary effects derived from Morris method to quantify their interaction. The findings reveal that ϑ exhibits a non-monotonic impact, whereas the influence of Dcav is monotonic but non-linear. The optimal ϑ is found to be within the range of 30–50 %, while the lowest Dcav mostly outperforms other values, contrary to previous studies. This deviation is speculated to arise from the consideration of hot air generation energy. Furthermore, the variation of one factor can potentially alter the optimal value of the other. The second-order elementary effect between them demonstrates that their coupling effect is also non-linear and non-monotonic, with an impact as significant as that of Dcav alone. Overall, the correlations between ϑ and Dcav should be thoroughly considered during the design period.

Micro/Meso-Porous Double-Shell Hollow Carbon Spheres through Spatially Confined Pyrolysis for Supercapacitors and Zinc-Ion Capacitor.

Energy storage in supercapacitors and hybrid zinc ion capacitors (ZIC) using porous carbon materials offers a promising alternative method for clean energy solutions. The unique combination of hierarchical porous structure and nitrogen doping in these materials has demonstrated significant capacity for energy storage. Nevertheless, the full potential of these materials, particularly the relationship between pore structure configuration and performance, remains underexplored. Herein, a confined pyrolysis strategy based on the polymerization characteristics of polydopamine (PDA) was developed to construction of hollow carbon spheres with microporous/mesoporous dual shell structure. The depth of micropores and cavity can be controlled by adjusting the duration of heat treatment and hydrothermal treatment, in accordance with the decomposition and polymerization characteristics of PDA. Due to the elasticity of this structure, the relationship between the micro/mesoporous depth of the prepared carbon spheres and the energy storage performance in supercapacitors and ZIC is established. Through optimizing the ion transport capacity of carbon spheres and considering the influence of its internal cavity structure on energy storage, the resulting carbon spheres exhibit high specific capacitance of 389 F g-1 in supercapacitor and specific capacitance of 260 F g-1 and excellent stability with 99.3 % retention after 30000 chare/discharge cycles in ZIC.

Influence of cavity geometry on the bubble dynamics of nucleate pool boiling

Nucleate pool boiling is known for its exceptional heat transfer coefficients, with the use of cavities further improving bubble nucleation and heat transfer rate. To promote this heat transfer enhancement technique, a thorough understanding of the influence of cavity geometry on single bubble dynamics is required. The influence of depth and radius of cylindrical and conical cavities on the bubble dynamics of nucleate pool boiling of R1234yf were numerically investigated. The cavity radius was varied between 50 and 400 μm and the cavity depth between 100 and 1000 μm at a fixed heat flux of 28 kW/m2. It was found that the maximum equivalent diameter prior to departure was constant for cavities with radii smaller than 120 μm, while it increased linearly when increasing the cavity radius further. Cylindrical cavities exhibited high stability regardless of cavity radius or depth whereas conical cavities showed a decrease in vapor retention with increasing cavity angle. During the necking phase, the bubble interface became pinned at the cavity edge, depending on conical cavity angle, implying that smaller radii allowed for enhanced surface rewetting. Conical cavities could be considered as cylindrical cavities when the cavity angle was less than a quarter of the interface contact angle. When translating the single cavity findings to cavity array design, cylindrical cavities were recommended as they allowed for stable bubble behavior. For increased nucleation zones and rewetting, a sub-critical radius was recommended. Wider cavities were recommended for high superheat conditions as larger bubbles could enhance bubble growth.

Pan‐Antarctic Assessment of Ice Shelf Flexural Responses to Ocean Waves

AbstractUnderstanding the drivers of iceberg calving from Antarctic ice shelves is important for future sea level rise projections. Ocean waves promote calving by imposing stresses and strains on the shelves. Previous modeling studies of ice shelf responses to ocean waves have focused on highly idealized geometries with uniform ice thickness and a flat seabed. This study leverages on a recently developed mathematical model that incorporates spatially varying geometries, combined with measured ice shelf thickness and seabed profiles, to conduct a statistical assessment of how 15 Antarctic ice shelves respond to ocean waves over a broad range of relevant wave periods, from swell to infragravity waves to very long period waves. The results show the most extreme responses at a given wave period are generated by features in the ice shelves and/or seabed geometries, depending on the wave regime. Relationships are determined between the median ice shelf response and the median shelf front thickness or the median water cavity depth. The findings provide further evidence of the role of ocean waves in large‐scale calving events for certain ice shelves (particularly the Wilkins) and indicate a possible role of ocean waves in calving events for other shelves (Larsen C and Conger). Further, the relationships determined provide a method to assess the potential for increased calving as ice shelves evolve with climate change, and, hence, contribute to assessments of future sea level rise.

Clinical Efficacy of a Novel Titania Nanoparticle-Reinforced Bonding Agent in Reducing Post-Restorative Sensitivity: A randomized clinical trial.

To evaluate the clinical efficacy of novel titania-nanoparticle reinforced bonding agent on post-restorative sensitivity in patients. This triple-blinded, randomized clinical trial included participants (n = 60) having Class- I and II cavitations with a minimum cavity depth of 3mm at Department of Operative Dentistry & Endodontics, School of Dentistry, Shaheed Zulfiqar Ali Bhutto Medical University, Islamabad from January 5, 2023, to June 20, 2023. They were randomly assigned into two groups A and B (n = 30). After informed consent, restorative intervention was accomplished using an etch-and-rinse adhesive strategy. In Group-A, titania-nanoparticle-incorporated bonding agent was used for composite restoration, while in Group-B, bonding agent without nanoparticles was used. The primary outcome was assessed using Visual Analogue Scale mean score. Participants were instructed to rate their sensitivity status at follow-ups: 24 hours, one week, and one month. Mann-Whitney U test was employed to compare sensitivity between the two groups. According to results of this trial, a significant difference was observed between two groups after 24 hours (p = 0.004) and one week (p = 0.002). However, no discernible difference was observed after one month (p = 0.643). Post-restorative sensitivity in patients with composite restorations was reduced using titania-reinforced bonding agents as compared to bonding agents without nanoparticles. This shows that inclusion of titania nanoparticles into adhesive dentistry could be beneficial in resolving post-restorative sensitivity occurring with composite restorations.

Research on wavelet packet energy entropy extraction method for acoustic signal of tunnel lining cavity

Abstract Tunnel lining cavity is a common disease in high-speed railway tunnels, which seriously affects the safe operation of the line.At present, the commonly used method is manual knocking inspection, but it relies on manual judgment, subjective factors have great influence, and there are errors. This paper proposes a feature extraction method of acoustic vibration signal of tunnel lining cavity based on wavelet packet energy entropy and uses wavelet packet energy entropy to realize the identification of cavity defects.The full-scale simulation model of tunnel with a radius of 6m was constructed by COMSOL and different cavity conditions were set up. The wavelet packet energy entropy characteristics of acoustic signals were extracted and analyzed. The mapping relationship between cavity depth and cavity size and wavelet packet energy entropy was explored. The wavelet packet energy entropy and frequency band distribution characteristics were extracted to realize the identification of cavity defects.The local model which can characterize the whole tunnel is designed and the embedded defects are verified by experiments. The results show that the wavelet packet energy entropy can be used as the identification feature of tunnel lining cavity defects. When the wavelet packet energy entropy is less than 2.53, the existence of tunnel lining cavity defects is characterized.When the wavelet packet energy entropy is in the range of 2.53-2.94, it characterizes the existence of the transition boundary between tunnel lining cavity defect and no disease.This index can be used to realize the rapid and effective identification of cavity defects.

Computationally Efficient Emulation of Spheroidal Elastic Deformation Sources Using Machine Learning Models: A Gaussian‐Process‐Based Approach

AbstractElastic continuum mechanical models are widely used to compute deformations due to pressure changes in buried cavities, such as magma reservoirs. In general, analytical models are fast but can be inaccurate as they do not correctly satisfy boundary conditions for many geometries, while numerical models are slow and may require specialized expertise and software. To overcome these limitations, we trained supervised machine learning emulators (model surrogates) based on parallel partial Gaussian processes which predict the output of a finite element numerical model with high fidelity but >1,000× greater computational efficiency. The emulators are based on generalized nondimensional forms of governing equations for finite non‐dipping spheroidal cavities in elastic halfspaces. Either cavity volume change or uniform pressure change boundary conditions can be specified, and the models predict both surface displacements and cavity (pore) compressibility. Because of their computational efficiency, using the emulators as numerical model surrogates can greatly accelerate data inversion algorithms such as those employing Bayesian Markov chain Monte Carlo sampling. The emulators also permit a comprehensive evaluation of how displacements and cavity compressibility vary with geometry and material properties, revealing the limitations of analytical models. Our open‐source emulator code can be utilized without finite element software, is suitable for a wide range of cavity geometries and depths, includes an estimate of uncertainties associated with emulation, and can be used to train new emulators for different source geometries.

The two-cavity method for characterizing acoustical materials-an interlaboratory study

The study focuses on understanding the sound absorption and transmission characteristics of porous acoustical materials, which are determined by two key parameters independent of material thickness: characteristic impedance and propagation constant. These parameters can be characterized by testing a porous sample concept in a normal incidence impedance tube using either the two-thickness or the two-cavity method. In the two-thickness method, two samples of varying thicknesses are required. In contrast, the two-cavity method requires testing one sample at two air cavity depths. This method is particularly advantageous for materials that are costly or challenging to fabricate. This interlaboratory study evaluates the variability of characteristic properties determined using the two-cavity method. Porous acoustical materials were additively manufactured and tested in the Liner Technology Facility at NASA Langley Research Center and the Mechanics, Acoustics and Dynamics Lab (MADLab) at Michigan Technological University. The characteristic properties, derived from various cavity depth combinations, were used to predict the sound absorption curves of the sample with a rigid backing. These predictions were then compared with actual experimental absorption curves. The findings indicate that both the combinations of cavity depths and the sample's static airflow resistivity significantly influence the accuracy of the deduced properties.

Clinical Performance of Computer-Aided Design (CAD)/Computer-Aided Manufacturing (CAM) Resin Nanoceramic Endocrowns in Restoring Molars: An In Vivo Study.

Background It is difficult to determine the optimal method for restoring endodontically treated teeth, as several factors affect this decision. Functional requirements and the amount of remaining coronal tissue are considered the most important factors in choosing the best restoration for those teeth. Endocrown was introduced as a conservative alternative for endodontically treated and coronally damaged teeth. Aim The aim of this study is to assess the clinical performance of the nanoceramic system for molar endocrowns by evaluating color change, gingival condition, prosthesis integrity, and the presence of secondary caries. Materials and methods The sample consisted of 20 endocrowns. The teeth were prepared with at least 2 mm of wall thickness and a cavity depth of 4 mm from the occlusal surface. The final impression was taken, and the prostheses were adhered using dual-cure resin cement. It was clinically evaluated according to clinical success criteria (United States Public Health Service) in terms of color stability, gingival indexes, integrity of the restoration, and the presence of secondary caries after a week, three months, six months, and a year. The statistical study was conducted using IBM SPSS Statistics for Windows, Version 23.0 (Released 2015; IBM Corp., Armonk, NY, USA), and the results were considered statistically significant at the 95% level of significance. The Friedman test was used to study the significance of the differences in the average values of color change, plaque index, and the integrity of the prostheses during follow-up periods. Results The study showed a gradual increase in the degree of color change with follow-up periods. Furthermore, there was no significant difference in the incidence of gingival changes, the integrity of the prosthetic margins, or the occurrence of secondary caries during the follow-up periods. Conclusions Within the limitations of this study, an endocrown made of CeraSmart nanoceramic is an acceptable option for crowning decayed and endodontic-treated molars with acceptable clinical performance.

Morphological differences between the lesser and the greater omenta in albino rats

BackgroundPublications report that all mammals have two omenta, namely, lesser omentum and greater omentum. Basically, these organs, which share the same name except for the adjective “lesser” or “greater,” should not differ from each other. However, no clear description of the structure of the lesser omentum, as well as comparative morphological analysis between the lesser and greater omenta have been found in the literature, which necessitates a thorough investigation. Therefore, the aim of our study was to analyze the morphofunctional differences between the greater and lesser omenta in albino rats. MethodThe experiment involved 20 mature male albino rats, weighing 298,28±7,36 grams. The material for our study were preparations of lesser and greater omenta, fixed in 10 % of neutral buffered formalin. Paraffin sections were stained with hematoxylin-eosin and Van Gieson stain. ResultsThe findings of the study showed that the greater omentum in albino rats, unlike other derivatives of the omentum (ligaments and mesenteries), represents a free extension (mostly from the greater curvature of the stomach), in the form of an “apron,” into a specific depth of the peritoneal cavity, duplicating the serous membrane. This duplication is characterized by the composition of two structurally interdependent formations. These include vascular-fatty arcades, associated with lymphoid nodules known as milky spots, and binding serous-reticular membranes. The findings of the study of the lesser omentum have established that in all cases it is located beneath the liver and becomes visualized only after hepatolifting. It is presented in the form of two ligaments: hepatoduodenal and hepatogastric, which contain two main structured formations, which we called vascular-fatty spurs, between these spurs, serous-reticular membranes are located. Conclusiondespite having similar names, the lesser omentum, a derivative of the peritoneum, is fundamentally different. As it is well known, the lesser omentum is represented by ligaments that extend from the liver hilus to the lesser curvature of the stomach and the duodenum. Due to this arrangement, the lesser omentum lacks the mobile activity characteristic of the greater omentum, which plays a crucial role in rapid response to damage in the gastrointestinal tract. Despite sharing the same names, both formations differ in shape, morphological structure, development and function

Flow dynamics and mixing of jet in crossflow with cylindrical cavity

The flow dynamics and mixing characteristics of an air jet issued from a cylindrical cavity in an air crossflow are numerically studied using a large-eddy-simulation technique. The cavity, aligned concentrically with the jet, is located beneath the crossflow wall. The jet-to-crossflow velocity ratio is 4, and the Reynolds number for the jet flow is 1.39×104 based on its diameter and centerline velocity. The presence of the cavity significantly influences the early evolution of the jet and its interaction with the crossflow. Complex vortical structures are observed. Notably, windward vortices on the jet surface increase in size, accompanied by a reduction in the Strouhal number. For a deep cavity, these vortices break down and result in small vortical tubes in the jet streamwise direction due to secondary instability. Also examined are leeward shear-layer vortices, hanging vortices, wake vortices, and the recirculating flow within the cavity. Their roles in the mixing between the jet fluid and the crossflow are identified. The cavity enhances mixing. The effect is significant in the near field but diminishes in the far field. By adjusting the cavity radius and depth, it is determined that the cavity depth exercises a more profound impact on jet evolution and mixing than the cavity radius. The most substantial influence occurs when a narrow and deep cavity is implemented. These findings may serve as guidelines for optimizing cavity design for effective modulation of jet behaviors.

Tunable plasmonic tweezers based on nanocavity array structure for multi-site nanoscale particles trapping

The ability of plasmonic optical tweezers based on metal nanostructure to stably trap and dynamically manipulate nanoscale objects at low laser power has been widely used in the fields of nanotechnology and life sciences. In particular, their plasmonic nanocavity structure can improve the local field intensity and trap depth by confining electromagnetic fields to subwavelength volumes. In this paper, the R6G dye molecules with 10−6 M were successfully trapped by using the Ag@Polydimethylsiloxane nanocavity array structure, and a R6G micro-ring was formed under the combined action of plasmonic optical force and thermophoresis. Subsequently, the theoretical investigation revealed that the trapping performance can be flexibly adjusted by changing the structural parameters of the conical nanocavity unit, and it can provide a stable potential well for polystyrene particles of RNP = 14 nm when the cavity depth is 140 nm. In addition, it is found that multiple trapping sites can be activated simultaneously in the laser irradiation area by investigating the trapping properties of the hexagonal conical nanocavity array structure. This multi-site stable trapping platform makes it possible to analyze multiple target particles contemporaneously.

Effects of blowing ratio and film hole arrangement on cavity blade tip cooling

Blade tip leakage is responsible for reducing the aerodynamic performance and increasing the thermal load. In order to obtain better cooling efficiency, the thermodynamic performance of different film hole arrangements and blowing ratios have been compared and analyzed in a cavity tip structure. Reynolds-averaged Navier–Stokes equation simulations at five blowing ratios from 0.25 to 2.0 have been carried out for three stream-wise and four pitch-wise film hole arrangements. Based on the reference flow field of the cavity without any coolant, the mechanism of the cooling air influence is analyzed by investigating the flow structure and the vortex development in the tip region. It is found that in the stream-wise arrangements and pitch-wise arrangements, the scheme SW1, in which the film holes are arranged along the suction surface, and the scheme PW2, in which the air film holes are arranged at 0.2 times the axial position, provide the maximum average film cooling efficiency of 0.235 and 0.282, respectively. However, the effective cooling area of SW1 is greater than that of PW2, which are 39.2% and 41.3%, respectively. At the lower blowing ratios, the cooling efficiency increases with the increase in the blowing ratio; however, at the higher blowing ratios, the cooling effect is affected by the clearance size and cavity depth when the coolant impinges on the casing wall.

The design method and test of a Dual-Focused ultrasound transducer toward small and adjustable F-numbers

An ultrasound transducer with a F-number less than 1.0 has been used in many fields such as non-destructive testing, medical treatment, particle manipulation, and so on. Traditional focusing technologies such as self-focusing structure and lens sets suffer from undesired surface cavitation due to large cavity depth, difficulties in fabrication, and most of designs have a fixed focal depth. This paper presents a small F-number ultrasound transducer design using a combination of acoustic lens and phased array, its fabrication process is not complicated, and focal depth is adjustable when applying different time delays. The design methods, including analytical expression, empirical equation and numerical results, are elaborated in this paper, followed by fabrication and tests. Simulations and experimental results prove that this dual-focused transducer can reach a changeable F-number as small as 0.72. The cavity depth of the transducer is relatively small (1.1 λ) compared to existing focusing transducers (4 ∼ 10 λ), which is not prone to unexpected surface cavitation. Moreover, the array in transducer has no grating lobes with an expanded pitch of 1.43 λ, which not only increase the fill factor and effective area but also further reduces the fabrication difficulty, especially in high frequency applications.

Method for evaluating and measuring cavity suitability for nesting wood ducks

AbstractThe challenges associated with climbing trees to measure cavity dimensions have limited the accumulation of knowledge regarding wood duck (Aix sponsa) nesting habitat and ecology. To overcome this issue, we developed a 2‐person method to measure external and internal tree‐cavity dimensions from the ground. Our approach uses a telescopic pole, wireless cavity inspection camera with a monitor, and reference scale, allowing an object of known length to be viewed and recorded inside the cavity. We tested our method using simulated cavities (n = 20), assessed accuracy by comparing the estimated and actual measurements, and evaluated precision between 2 observers. The average difference (±1 SE) between estimated and actual measurements (n = 40) for entrance width (0.9 ± 0.9 cm), entrance height (0.8 ± 1.1 cm), platform width (0.1 ± 3.7 cm), and platform length (1.0 ± 3.2 cm) were ≤1 cm. There was no significant difference between observer measurements for entrance width, entrance height, platform width, or platform length. Observers overestimated cavity depth by an average of 0.1 ± 1.6 cm and there was a significant difference (1.3 ± 2.2 cm) between observers for mean cavity depth. We applied the technique to naturally occurring cavities. The time to complete a natural‐cavity survey in the field (n = 37) averaged 12.2 ± 6.9 min. Our method increases the practicality, accessibility, and safety of researchers conducting cavity surveys for wood ducks and other cavity‐dependent wildlife through the use of a cost‐effective, cavity‐measuring tool.

Acoustic properties of a micro-perforated muffler with parallel-arranged cavities of different depths

Low-frequency noise generated by ventilation systems propagates into indoor environment through ducts. In this study, a novel micro-perforated panel (MPP) muffler, with the absence of porous material in cavities, backed radially with parallel-arranged cavities of different depths (PCD) is proposed. Based on the two-load method, numerical simulations and experiments are conducted to evaluate sound transmission loss (TL) and sound wave radiating coefficients (SWRC) of the PCD-MPP muffler. Influences of muffler parameters on TL and SWRC are then discussed by numerical simulation. A wideband compound PCD-MPP muffler with high performance is finally proposed. Results show that the numerical model provides accurate prediction on acoustic properties of the PCD-MPP muffler by comparing with the results by experiments. Numerical results demonstrate that, the coupling effect of absorption resonance occurred by cavities of different depths contributes to the wideband silencing performance. TL, absorptance and reflectance improve when enhancing the length of the muffler, while TL and absorptance move to lower frequencies with the increase of cavity depth. In addition, TL of the compound PCD-MPP muffler is higher than 20 dB within the frequency range of 700–1600 Hz, with a maximum TL of 42.5 dB. The present work also highlights the higher TL and absorptance than other types of MPP mufflers, and silencing performance can be customized by adjusting the perforation parameters and cavity depths, which may provide a valuable reference in ventilation noise reduction with the absence of porous material.

Efficacy of hysteroscopic levonorgestrel‑releasing intrauterine device fixation in the treatment of adenomyosis: A cohort study.

The present study aimed to investigate the efficacy of hysteroscopic levonorgestrel-releasing intrauterine device (LNG-IUD) fixation surgery in the treatment of adenomyosis through a cohort study. The cohort study was performed at the Affiliated Jinhua Hospital of Wenzhou Medical University (Jinhua, China). A total of 31 women with adenomyosis were initially recruited from June 2020 to June 2022 and divided into an experimental group and a control group. The experimental group underwent hysteroscopic LNG-IUD fixation surgery and the control group underwent conventional implantation of the levonorgestrel-releasing intrauterine system. The assessed efficacy outcomes included the time of LNG-IUD expulsion, postoperative vaginal bleeding time, dysmenorrhea, and the menstrual blood loss score (MBLS). A total of 31 participants completed the research. The LNG-IUD expulsion rate was 6.25 and 60% (P<0.05) in the experimental and control group, respectively. The LNG-IUD in place time was 20.50 months (Q1, 15.75; Q3, 24.00) in the experimental group and 10.00 months (Q1, 6.50; Q3, 15.00) in the control group (P<0.05); the time of vaginal bleeding after surgery in the experimental and control groups were 12.50 days (9.25, 16.25) and 120.00 days (75.00, 120.00), respectively (P<0.05). Multiple-factor Cox regression analysis revealed that the LNG-IUD expulsion in patients with adenomyosis is associated with the hysteroscopic LNG-IUD fixation surgery [hazard ratio (HR), 1954.09], uterine cavity depth (HR, 16.63), MBLS (HR, 1.14), history of gonadotropin-releasing hormone agonist treatment in the previous 6 months (HR, 2.10), history of vaginal delivery (HR, 1.79) and history of cervical laceration (HR, 3.69). In conclusion, hysteroscopic LNG-IUD fixation reduces the rate of LNG-IUD expulsion, prolongs the time of LNG-IUD in the uterine cavity, reduces the time of postoperative vaginal bleeding, relieves the symptoms of dysmenorrhea and reduces the menstrual volume in the patients with adenomyosis. The present trial was retrospectively registered in the Chinese Clinical Trial Registry on 28th December 2023 (registration no. ChiCTR2300079233).

Unsteady flow behaviors and flow-induced noise characteristics in a closed branch T-junction

In the present study, dynamic delayed detached eddy simulation is utilized to explore turbulent flow in T-junctions at a Reynolds number of ReD = 2.0 × 104. Three systems with varying corner cavity depth-to-diameter ratios (Ld/D = 1, 2, and 4) are examined to elucidate the interplay between unsteady flow and flow-induced noise. The analysis employs Lighthill's acoustic analogy to scrutinize surface dipole acoustic sources and their noise propagation characteristics. Coherent flow structures, characterized as wavepackets, are identified through spectral proper orthogonal decomposition, demonstrating consistent dominance in modes and dipole distributions across the systems. In the system with Ld/D = 1, wavepackets originating from the downstream region of the junction exhibit a pronounced flapping behavior attributed to the Kelvin–Helmholtz instability. Most dissipate with the mainstream flow, whereas a portion interacts with the wall, forming dipole acoustic sources. For systems with Ld/D = 2 and 4, the dominant mode transitions to the junction adjacent to the corner cavity, expanding continuously after separation until obliquely colliding with the wall, resulting in expanded dipole distributions. Mechanisms underlying flow-induced noise generation are unveiled by extracting transient vorticity fields within oscillation cycles. For shallow corner cavity depths (Ld/D = 1), periodic oscillatory vorticity shedding from the junction's sidewall significantly contributes to far-field sound pressure. As the cavity is deep enough to support one or more full recirculations of the fluid (Ld/D = 2 and 4), periodic vorticity shedding from the trailing edge directly impacts the wall above the junction, simultaneously suppressing flapping behavior at the leading edge and weakening overall dipole acoustic source intensity.

Rectangular extended neck Helmholtz resonant acoustic structure for low frequency broadband sound absorption

The Helmholtz resonant structure with rectangular extended neck is designed to solve low-frequency broadband sound absorption problem in this work. Theoretical and finite element absorption models are established and be used for low-frequency acoustic design. What makes it interesting is that all parameters of the rectangular extended neck Helmholtz resonator structure can be adjusted to shift the working frequency. Based on the regularity of the structural parameters, four coupling structures with different neck depths, neck opening areas, cavity cross-sectional areas, and cavity depths are designed respectively, each of which exhibited multiple sound absorption coefficient peaks to enhance the low-frequency absorption capacity of the structure. To further analyze the effectiveness of coupling structure, the broadband acoustic absorption mechanism of the coupled structure is analyzed based on particle vibration velocity distribution. It is found that cells with different acoustic impedance contributed differently to the sound absorption, and cells with longer necks provided better noise reduction for low-frequency. The experiment is verified in the impedance tube, result shows that the coupling structure with 9 cells and a cavity depth of only 4 cm achieved an average sound absorption coefficient of above 0.8 at 210–340 Hz, which verified the accuracy of the theoretical model. Overall, the Helmholtz resonant cavity acoustic structure with rectangular extension neck designed in this work has a simple structure with low-frequency broadband acoustic absorption performance. This provides a new approach for designing low-frequency broadband acoustic structure.

A Comprehensive Study of NF3-Based Selective Etching Processes: Application to the Fabrication of Vertically Stacked Horizontal Gate-All-around Si Nanosheet Transistors.

In this paper, we demonstrate a comprehensive study of NF3-based selective etching processes for inner spacer formation and for channel release, enabling stacked horizontal gate-all-around Si nanosheet transistor architectures. A cyclic etching process consisting of an oxidation treatment step and an etching step is proposed and used for SiGe selective etching. The cyclic etching process exhibits a slower etching rate and higher etching selectivity compared to the direct etching process. The cycle etching process consisting of Recipe 1, which has a SiGe etching rate of 0.98 nm/cycle, is used for the cavity etch. The process achieved good interlayer uniformity of cavity depth (cavity depth ≤ 5 ± 0.3 nm), while also obtaining a near-ideal rectangular SiGe etch front shape (inner spacer shape = 0.84) and little Si loss (0.44 nm@ each side). The cycle etching process consisting of Recipe 4 with extremely high etching selectivity is used for channel release. The process realizes the channel release of nanosheets with a multi-width from 30 nm to 80 nm with little Si loss. In addition, a selective isotropic etching process using NF3/O2/Ar gas mixture is used to etch back the SiN film. The impact of the O2/NF3 ratio on the etching selectivity of SiN to Si and the surface roughness of SiN after etching is investigated. With the introduction of O2 into NF3/Ar discharge, the selectivity increases sharply, but when the ratio of O2/NF3 is up to 1.0, the selectivity tends to a constant value and the surface roughness of SiN increases rapidly. The optimal parameter is O2/NF3 = 0.5, resulting in a selectivity of 5.4 and a roughness of 0.19 nm.