Impacts of spatial symmetries on stimulated Brillouin scatterings in nanoscale silicon waveguides: a theoretical and numerical study considering material anisotropies.

Fully considering the mechanical and photoelastic anisotropies of monocrystalline silicon, the impacts of spatial symmetries on the stimulated Brillouin scatterings (SBSs) in nanoscale suspended silicon waveguides are studied theoretically and numerically based on group theory. First, starting from an assumption that the principal material coordinate system can be arbitrarily orientated in a waveguide with fixed geometry, the silicon waveguides are systematically classified into a number of point groups according to their spatial symmetry features. Thereafter, the symmetry characteristics of physical fields and SBS opto-mechanical coupling characteristics in the silicon waveguides belonging to different point groups are further examined, and the major new findings can be summarized as follows: The SBS opto-mechanical couplings in several kinds of silicon waveguides with certain nontrivial symmetry features exhibit relatively predictable behaviors in that the opto-mechanical coupling coefficients can be deterministically vanishing or nonvanishing under very few constraints, which can thus serve as general symmetry selection rules for SBSs in suspended silicon waveguides. The results obtained in the present study could be a useful theoretical reference for the design of novel SBS-active silicon photonic devices.

Design of microperforated nanofibrous membrane coated nonwoven structure for acoustic applications.

In this paper, a promising acoustic structure for noise reduction was prepared, in which microperforated nanofibrous resonant membrane together with nonwovens were used. The role of microperforated nanofibrous film, the effect of perforation parameters, cavity and the assembly sequence of the composite fibrous structure on sound absorption performance has been studied. This structure effectively combined the porous sound absorbing, micro-perforated absorbing and membrane resonance mechanisms, which can improve the sound absorbing performance without weight and thickness penalty offering a competitive advantage in noise reduction. In addition, the composite materials exhibited favorable performance in a wide-frequency regime under the condition of appropriate assembly sequence and perforation parameters.

Assessment of in-cabin noise of wide-body aircrafts.

The aviation industry has seen dramatic growth over the decades till the recent disruption due to the COVID-19 pandemic. Moreover, long-haul routes with a distance of more than 4000 km are common for major airlines worldwide. Therefore, aircraft cabin noise assessment is essential, especially in long-haul flights, for passenger and flight crew health wellness. In this paper, the cabin noise of five wide-body aircraft, namely Airbus A330-300ER, A350-900, A380-800, and Boeing B777-200ER and B787-900, was recorded using a calibrated in-house developed smartphone application. The sound pressure levels of in-cabin noise have been measured on two different decibel scales, namely, A-weighted [dB(A)] and C-weighted scales [dB(C)]. The sound pressure levels of Airbus A380-800 were lowest among selected models, while the in-cabin pressure level values of Airbus A350-900 were maximum. However, the difference in decibel levels between the aircraft is minimal as it is within 3 dB.

Microlattice Metamaterials with Simultaneous Superior Acoustic and Mechanical Energy Absorption.

The advent of 3D printing brought about the possibilities of microlattice metamaterials as advanced materials with the potentials to surpass the functionalities of traditional materials. Sound absorbing materials which are also tough and lightweight are of particular importance as practical engineering materials. There are however a lack of attempts on the study of metamaterials multifunctional for both purposes. Herein, we present four types of face-centered cubic based plate and truss microlattices as novel metamaterials with simultaneous excellent sound and mechanical energy absorption performance. High sound absorption coefficients nearing 1 and high specific energy absorption of 50.3 J g-1 have been measured. Sound absorption mechanisms of microlattices are proposed to be based on a "cascading resonant cells theory", an extension of the Helmholtz resonance principle that we have conceptualized herein. Characteristics of absorption coefficients are found to be essentially geometry limited by the pore and cavity morphologies. The excellent mechanical properties in turn derive from both the approximate membrane stress state of the plate architecture and the excellent ductility and strength of the base material. Overall, this work presents a new concept on the specific structural design and materials selection for architectured metamaterials with dual sound and mechanical energy absorption capabilities.

Mitigating the toilet flush noise: A psychometric analysis of noise assessment and design of labyrinthine acoustic Meta-absorber for noise mitigation.

Modern apartments in major cities are usually made of lightweight structures with inadequate acoustic properties, leading to a growing number of noise complaints by residents of inadequate sound insulation in high-rise buildings. When a toilet is flushed, loud and irregular sounds like humming, gurgling, or bubbling, "explosive" fury from vacuum-assisted toilets are generated. Though these toilet flushing sounds are not very harmful, they can still be perceived as nuisances by users nearby. The toilet flushing noise has posed a serious concern among apartment occupants and adjacent residents, causing health problems like sleep disturbance and irritation. In this study, the psychoacoustical investigations have been performed in four stages. In the first stage, the toilet flushing noise was recorded for several toilets with two designs: a close-coupled floor-mount toilet and a back-to-wall mount toilet. The second stage evaluated the physical and psychoacoustical characteristics of those recorded flushing sounds using psychoacoustic analysis software. The noise qualities were determined in the third stage by assessing autocorrelation function/interaural cross correlation function factors from the post-processed recorded sound data. Finally, we designed and successfully demonstrated an innovative acoustic meta-absorber prototype for mitigating the toilet flushing noise. The results have revealed a significant reduction in loudness because of meta-absorbers.

A theoretical and numerical study on the mechanics of vibro-acoustic modulation.

Vibro-acoustic modulation (VAM) is a form of a non-destructive testing technique used in nonlinear acoustic methods for the detection of defects. It comprises of exciting the structure with a dual frequency sinusoidal signal and studying the interaction of this wave with the underlying defect. In this work a theoretical study on the mechanics of VAM is presented for a generic material body. The roles of different types of defect on the response of the material are analyzed. The theoretical analysis shows the origins of the nonlinear frequencies in the form of higher harmonics and sidebands commonly observed in the output response of VAM excitation. In addition, the analysis provides insights on the relationships between the magnitudes of the nonlinear responses and those of the input vibrations, and on the physical origins of the nonlinear responses. For a physical visualization of the nonlinear vibrations associated with the theory a finite element analysis of VAM is also performed. The model looks into the plausibility of using VAM for the mapping of damage in physical structures. The model is also used to investigate the effects of the defect size and defect depth on the nonlinear mechanism of VAM.

Empirical concentration bounds for compressive holographic bubble imaging based on a Mie scattering model.

We use compressive in-line holography to image air bubbles in water and investigate the effect of bubble concentration on reconstruction performance by simulation. Our forward model treats bubbles as finite spheres and uses Mie scattering to compute the scattered field in a physically rigorous manner. Although no simple analytical bounds on maximum concentration can be derived within the classical compressed sensing framework due to the complexity of the forward model, the receiver operating characteristic (ROC) curves in our simulation provide an empirical concentration bound for accurate bubble detection by compressive holography at different noise levels, resulting in a maximum tolerable concentration much higher than the traditional back-propagation method.

Similar Fracture Patterns in Human Nose and Gothic Cathedral.

This study proposes that the bony anatomy of the human nose and masonry structure of the Gothic cathedral are geometrically similar, and have common fracture patterns. We also aim to correlate the fracture patterns observed in patients' midface structures with those seen in the Gothic cathedral using computational approach. CT scans of 33 patients with facial fractures were examined and compared with computer simulations of both the Gothic cathedral and human nose. Three similar patterns were found: (1) Cracks of the nasal arch with crumpling of the vertical buttresses akin to the damage seen during minor earthquakes; (2) lateral deviation of the central nasal arch and collapse of the vertical buttresses akin to those due to lateral forces from wind and in major earthquakes; and (3) Central arch collapse seen as a result of collapse under excessive dead weight. Interestingly, the finding of occult nasal and septal fractures in the mandible fractures with absence of direct nasal trauma highlights the possibility of transmission of forces from the foundation to the arch leading to structural failure. It was also found that the structural buttresses of the Gothic cathedral delineate the vertical buttresses in the human midface structure. These morphologic similarities between the human nose and Gothic cathedral will serve as a basis to study the biomechanics of nasal fractures. Identification of structural buttresses in a skeletal structure has important implications for reconstruction as reestablishment of structural continuity restores normal anatomy and architectural stability of the human midface structure.

Computer-Aided Analysis of the "Beautiful" Umbilicus.

BACKGROUND: The position, shape, size, and depth of the umbilicus influence the overall aesthetics of the abdomen. Hence, umbilicoplasty is a common adjunct to aesthetic and reconstructive surgery of the abdominal wall. Delineation of the position and shape of the "beautiful" umbilicus can aid in the planning of abdominoplasty and lipoabdominoplasty. OBJECTIVES: The authors aimed to identify key parameters of the beautiful umbilicus. METHODS: Previously, the authors developed software (the Aesthetic Analyzer) for marking and analyzing parameters from images of the nose, breast, and umbilicus. In the present study, the Aesthetic Analyzer was utilized to determine parameters of the beautiful umbilicus from images of 37 Playboy playmates. The vertical position, horizontal position, length, and shape of the umbilicus were assessed. RESULTS: Based on these images, the beautiful umbilicus possesses the following properties: a vertical ratio of 46:54 (with respect to the xiphoid process and lower limit of the vulvar cleft), a midline horizontal position, a length that is 5% of the length from the xiphoid process to the lower limit of the vulvar cleft, and an oval shape with no hooding (29.8%) or superior hooding (21.6%). CONCLUSIONS: Awareness of the ideal position, shape, and size of the umbilicus can be useful for achieving successful reconstruction of the umbilicus during abdominoplasty and lipoabdominoplasty.

Sustainable Sensing with Paper Microfluidics: Applications in Health, Environment, and Food Safety.

This manuscript offers a concise overview of paper microfluidics, emphasizing its sustainable sensing applications in healthcare, environmental monitoring, and food safety. Researchers have developed innovative sensing platforms for detecting pathogens, pollutants, and contaminants by leveraging the paper's unique properties, such as biodegradability and affordability. These portable, low-cost sensors facilitate rapid diagnostics and on-site analysis, making them invaluable tools for resource-limited settings. This review discusses the fabrication techniques, principles, and applications of paper microfluidics, showcasing its potential to address pressing challenges and enhance human health and environmental sustainability.

Review on the Advancements of Stethoscope Types in Chest Auscultation.

Stethoscopes were originally designed for the auscultation of a patient's chest for the purpose of listening to lung and heart sounds. These aid medical professionals in their evaluation of the cardiovascular and respiratory systems, as well as in other applications, such as listening to bowel sounds in the gastrointestinal system or assessing for vascular bruits. Listening to internal sounds during chest auscultation aids healthcare professionals in their diagnosis of a patient's illness. We performed an extensive literature review on the currently available stethoscopes specifically for use in chest auscultation. By understanding the specificities of the different stethoscopes available, healthcare professionals can capitalize on their beneficial features, to serve both clinical and educational purposes. Additionally, the ongoing COVID-19 pandemic has also highlighted the unique application of digital stethoscopes for telemedicine. Thus, the advantages and limitations of digital stethoscopes are reviewed. Lastly, to determine the best available stethoscopes in the healthcare industry, this literature review explored various benchmarking methods that can be used to identify areas of improvement for existing stethoscopes, as well as to serve as a standard for the general comparison of stethoscope quality. The potential use of digital stethoscopes for telemedicine amidst ongoing technological advancements in wearable sensors and modern communication facilities such as 5G are also discussed. Based on the ongoing trend in advancements in wearable technology, telemedicine, and smart hospitals, understanding the benefits and limitations of the digital stethoscope is an essential consideration for potential equipment deployment, especially during the height of the current COVID-19 pandemic and, more importantly, for future healthcare crises when human and resource mobility is restricted.

High resolution UV roll-to-roll nanoimprinting of resin moulds and subsequent replication via thermal nanoimprint lithography.

UV roll-to-roll nanoimprinting at high resolution is still a relatively unexplored field of study with far-reaching application potential. One enabling technology that is particularly worthy of attention is mass production of high resolution resin moulds via UV roll-to-roll nanoimprinting at such high throughput and low cost that they can be used only once and disposed of or recycled economically. Low cost, high resolution resin moulds can greatly improve the production cost profile for a number of applications in biomedicine, nanofluidics, data storage and electronics with relatively low unit values but which require one or more nanoscale lithography steps. In this report, UV roll-to-roll nanoimprinting was employed to fabricate high fidelity resin moulds with nanoscale as well as mixed micro- and nanoscale features down to 50 nm feature diameter, at up to 120 cm(2) area and at 10 m min(-1) throughput. UV roll-to-roll nanoimprinted resin moulds were subsequently segmented out, employed in a batch mode thermal nanoimprinting process, and characterized to study performance and demonstrate viability. The results show that high resolution mixed nanostructures can be faithfully replicated in PMMA on silicon substrates with minimal volumetric shrinkage. Process details and challenges specific to roll-to-roll fabrication of resin moulds are discussed at length, particularly with respect to the curvature uniformity of the imprint roller.

Characterization of kidney stones using thermogravimetric analysis with electron dispersive spectroscopy.

Urinary calculi are formed from a result of biological mal-adjustment of urine leading to deposits of salt and mineral crystals along the urinary collecting system. They are usually multiphasic material with complex compositions. The objective of this study is to identify and characterize a series of urinary calculi samples using a combination of thermogravimetric analysis (TGA) with electron dispersive spectroscopy (EDS). These samples were retrieved during percutaneous nephrolithotripsy. Additional characterization by hardness value and microstructure is also carried out for co-relation study. The samples are found to be uric acid, calcium oxalates and magnesium ammonium phosphate hexahydrate. TGA is indeed one of the viable analytical tools for urinary calculi as it is fast and simple. The combinational application of EDS is beneficial when there is a need for differentiated qualitative chemical composition detection at the identified nuclei position for urinary calculi with spatial variation in composition. The combination of TGA and EDS will thus facilitate the correct diagnosis and treatment by clinicians.

Inhibition of barnacle cyprid settlement using low frequency and intensity ultrasound.

Low frequency, low intensity ultrasound was demonstrated as an effective inhibitor of barnacle cyprid settlement. When the same substratum vibration amplitude (10.05 nm) and acoustic pressure (5 kPa) were applied, ultrasound at a frequency of 23 kHz significantly reduced cyprid settlement. The mechanism appeared to differ from the ultrasonic cavitation induced inhibition previously reported as no increased mortality was observed, and no change in the exploratory behaviour of cyprids was observed when they were exposed to this continuous ultrasonic irradiation regime. The application of ultrasound treatment in an intermittent mode of '5 min on and 20 min off' at 20-25 kHz and at the low intensity of 5 kPa produced the same effect as the continuous application of 23 kHz. This energy efficient approach to the use of low frequency, low intensity ultrasound may present a promising and efficient strategy regarding irradiation treatment for antifouling applications.

Effects of shear and surface roughness on reducing the attachment of Oscillatoria sp. filaments on substrates.

The effects of surface roughness and shear on the attachment of Oscillatoria sp. algal filaments onto SS314 stainless steel coupons were investigated. Average surface roughness was used to systematically characterize the surface condition. An annular biofilm reactor with a spinning inner cylinder was used to create a uniform shear flow over the coupons. As far as the authors are able to establish, these systematic methods have yet to be used in the study of microalgae deposition. It was postulated that increasing average surface roughness would lead to an increase in the amount of algae deposited, whereas an increase in shear would lead to a decrease in algae deposition and reduce the algae lengths by way of fragmentation. The results indicate that an increasing surface roughness would increase the amount of algal strands that might deposit on the coupons, whereas shear was found to have the effect of reducing the amount of algae that might attach on the coupons.

Effect of ultrasound on cyprids and juvenile barnacles.

Settlement inhibition of barnacle (Amphibalanus amphitrite) cypris larvae resulting from exposure to ultrasound was measured at three frequencies (23, 63, and 102 kHz), applied at three acoustic pressure levels (9, 15, and 22 kPa) for exposure times of 30, 150, and 300 s. The lowest settlement was observed for 23 kHz, which also induced the highest cyprid mortality. Cyprid settlement following exposure to 23 kHz at 22 kPa for 30 s was reduced by a factor of two. Observing surface exploration by the cyprids revealed an altered behaviour following exposure to ultrasound: step length was increased, while step duration, walking pace, and the fraction of cyprids exploring the surface were significantly reduced with respect to control cyprids. The basal area of juvenile barnacles, metamorphosed from ultrasound-treated cyprids was initially smaller than unexposed individuals, but normalised over two weeks' growth. Thus, ultrasound exposure effectively reduced cyprid settlement, yet metamorphosed barnacles grew normally.

Objective assessment of increase in breathing resistance of N95 respirators on human subjects.

Face masks or respirators are commonly worn by medical professionals and patients for protection against respiratory tract infection and the spread of illnesses, such as severe acute respiratory syndrome and pandemic influenza (H1N1). Breathing discomfort due to increased breathing resistance is known to be a problem with the use of N95 respirators but there is a lack of scientific data to quantify this effect. The purpose of this study was to assess objectively the impact of wearing N95 face masks on breathing resistance. A total of 14 normal adult volunteers (seven males and seven females) were recruited in this study. Nasal airflow resistance during inspiration and expiration was measured using a standard rhinomanometry and nasal spirometry. A modified full face mask was produced in-house in order to measure nasal resistance with the use of N95 (3M 8210) respirators. The results showed a mean increment of 126 and 122% in inspiratory and expiratory flow resistances, respectively, with the use of N95 respirators. There was also an average reduction of 37% in air exchange volume with the use of N95 respirators. This is the first reported study that demonstrates quantitatively and objectively the substantial impairment of nasal airflow in terms of increased breathing resistance with the use of N95 respirators on actual human subjects.

Mass transport in a microchannel bioreactor with a porous wall.

A two-dimensional flow model has been developed to simulate mass transport in a microchannel bioreactor with a porous wall. A two-domain approach, based on the finite volume method, was implemented. For the fluid part, the governing equation used was the Navier-Stokes equation; for the porous medium region, the generalized Darcy-Brinkman-Forchheimer extended model was used. For the porous-fluid interface, a stress jump condition was enforced with a continuity of normal stress, and the mass interfacial conditions were continuities of mass and mass flux. Two parameters were defined to characterize the mass transports in the fluid and porous regions. The porous Damkohler number is the ratio of consumption to diffusion of the substrates in the porous medium. The fluid Damkohler number is the ratio of the substrate consumption in the porous medium to the substrate convection in the fluid region. The concentration results were found to be well correlated by the use of a reaction-convection distance parameter, which incorporated the effects of axial distance, substrate consumption, and convection. The reactor efficiency reduced with reaction-convection distance parameter because of reduced reaction (or flux), and smaller local effectiveness factor due to the lower concentration in Michaelis-Menten type reactions. The reactor was more effective, and hence, more efficient with the smaller porous Damkohler number. The generalized results could find applications for the design of bioreactors with a porous wall.

Impact of inferior turbinate hypertrophy on the aerodynamic pattern and physiological functions of the turbulent airflow - a CFD simulation model.

INTRODUCTION: The aim of this study was to investigate the effects of nasal obstruction with enlargement of inferior turbinates on the aerodynamic flow pattern using Computational Fluid Dynamics (CFD) tools including the effects of turbulence. METHODS: A high-resolution 3-dimensional model of the nasal cavity was constructed from MRI scans of a healthy human subject using MIMICS 12.0 software. Nasal cavities corresponding to healthy, moderate and severe nasal obstructions were simulated by enlarging the inferior turbinate geometrically. Numerical simulations with turbulent flow models were implemented using FLUENTS for CFD simulations. RESULTS: In the healthy nose, the main respiratory air stream occurs mainly in the middle of the airway, accompanied by a diffused pattern of turbulent flow on the surface of the nasal mucosa. The peak value of turbulent flow is found in the functional nasal valve region. However, this aerodynamic flow pattern has partially or completely changed in the models with enlarged inferior turbinate. An inhalation flow rate of 34.8 L/min with a maximum velocity of 5.69 m/s, 7.39 m/s and 11.01 m/s are detected, respectively, in the healthy, moderately and severely obstructed noses. Both total negative pressure and maximum shear stress have increased by more than three and two times, respectively, in severely blocked noses compared to the healthy one. CONCLUSION: Data of this study provide quantitative and quantitative information of the impact of inferior turbinate hypertrophy on the aerodynamic pattern and physiological functions of nasal airflow. By including the model of turbulent airflow, the results of this experimental study will be more meaningful and useful in predicting the aerodynamic effects of surgical correction of inferior turbinate hypertrophy.