bluuebunny/crossref_metadata_2025 huggingface dataset:
A class of expansion functions for finite elastic plates in structural acoustics
Authors: Craster Richard V. , Llewellyn Smith Stefan G.
Published: July 2002

Problems in structural acoustics involving finite plates can be formulated using integral equation methods. The unknown function within the integral equation must satisfy the plate edge conditions, and hence appropriate expansion functions must be used. The expansion functions developed here are aimed at treating a wide class of problems. Once such functions are found, the solution process and numerical implementation are relatively straightforward. The speed of convergence to “exact” comparison solutions is fast even in the singular limit of high frequencies and wide plates. A set of expansion functions with the required properties is constructed and some illustrative problems are treated.
Nonlinear propagation of laser-generated sound pulses in a water and granular medium
Authors: Naugolnykh K. A. , Egerev S. V. , Esipov I. B. , Matveev K. A.
Published: July 2002

Nonlinear propagation of finite-amplitude acoustic pulse in water and through a sample of water-saturated granular medium is considered. To generate high-intensity acoustic pulses laser generation of sound was used. The region of fluid perturbed by the laser acts as a volume-distributed source. In a fluid with weak light attenuation, a cylindrical source could be formed by a narrow laser beam. The nonlinear distortion of the cylindrical finite-amplitude wave in water is investigated. The measured rate of distortion corresponds to that calculated in the approximation of nonlinear acoustics. In a strongly light-absorbing medium, a wide (compared to the typical sound wavelength) laser beam produces a circular planar source. Such a source produces acoustical pulses of amplitude up to 3 MPa and duration about 1 μs in different fluids. This source was used to investigate the propagation of high-intensity wide frequency band sound signals in a sample of water-saturated cobalt–manganese crust (CMC). Specific acoustical features of the crust such as nonlinear sound pulse distortion and the frequency dependance of attenuation, varying with the amplitude, are considered. Theoretical interpretation of the results is given.
Effects of frequency and duration on psychometric functions for detection of increments and decrements in sinusoids in noise
Authors: Moore Brian C. J. , Peters Robert W. , Glasberg Brian R.
Published: July 2002

Psychometric functions for detecting increments or decrements in level of sinusoidal pedestals were measured for increment and decrement durations of 5, 10, 20, 50, 100, and 200 ms and for frequencies of 250, 1000, and 4000 Hz. The sinusoids were presented in background noise intended to mask spectral splatter. A three-interval, three-alternative procedure was used. The results indicated that, for increments, the detectability index d′ was approximately proportional to ΔI/I. For decrements, d′ was approximately proportional to ΔL. The slopes of the psychometric functions increased (indicating better performance) with increasing frequency for both increments and decrements. For increments, the slopes increased with increasing increment duration up to 200 ms at 250 and 1000 Hz, but at 4000 Hz they increased only up to 50 ms. For decrements, the slopes increased for durations up to 50 ms, and then remained roughly constant, for all frequencies. For a center frequency of 250 Hz, the slopes of the psychometric functions for increment detection increased with duration more rapidly than predicted by a “multiple-looks” hypothesis, i.e., more rapidly than the square root of duration, for durations up to 50 ms. For center frequencies of 1000 and 4000 Hz, the slopes increased less rapidly than predicted by a multiple-looks hypothesis, for durations greater than about 20 ms. The slopes of the psychometric functions for decrement detection increased with decrement duration at a rate slightly greater than the square root of duration, for durations up to 50 ms, at all three frequencies. For greater durations, the increase in slope was less than proportional to the square root of duration. The results were analyzed using a model incorporating a simulated auditory filter, a compressive nonlinearity, a sliding temporal integrator, and a decision device based on a template mechanism. The model took into account the effects of both the external noise and an assumed internal noise. The model was able to account for the major features of the data for both increment and decrement detection.
Generation and maintenance of bubbles in small tubes by low-frequency ultrasound
Authors: Lam Kwok W. , Drake James M. , Cobbold Richard S. C.
Published: July 2002

A system has been developed to generate and maintain a bubble population in nonscattering fluid media within a small 1.3-mm (i.d.) transparent silicone tube by use of low-frequency ultrasound at 28.8 kHz. The system uses a sequence of three different kinds of acoustic cavitation processes: transient, stable and cyclic. In the final step of the sequence, low-duty cycle (∼10%) and low-pressure (∼30 kPa) ultrasound is used to maintain a microbubble population whose mean diameter is ∼12 μm, which can be used as Doppler ultrasound scatterers. To understand and measure the behavior of bubbles for three different kinds of cavitation processes in the tube, a CCD imaging system and a synchronized short duration flash were used to capture movie frame sequences. Subsequent analysis of the frames enabled the following bubble parameters to be measured: size distributions, fractional volume concentration, flow characteristics, rise velocity, dissolution time, growth rate and various bubble formation processes. In addition, the cavitation threshold of distilled water inside the tube was found to be ∼292±99 kPa. Techniques were also developed to identify successful bubble initiation and excitation by either detecting the harmonic components of the bubble emission power spectra or by detecting the power level of the Doppler spectrum.
On the effect of the bending vibration on the acoustic properties of thin poroelastic plates
Authors: Swift M. J. , Horoshenkov K. V. , Leclaire P. , Hothersall D. C. , Fujiwara K. , Torihama H.
Published: July 2002

An experimental study on the effect of bending vibration on the acoustic properties of thin porous plates is presented. Poroelastic plates are tested in a large impedance tube in the lower frequency range. It is shown that bending vibration can be excited by the incident sound and detected by measuring the acoustic impedance of a plate. This effect together with the effect of the flow resistivity on the values of the acoustic impedance of the plate are shown. The data from the large and small impedance tubes illustrate how these effects are reduced with the reduced size of the plate.
Three-dimensional acoustic scattering from a penetrable layered cylindrical obstacle in a horizontally stratified ocean waveguide
Authors: Athanassoulis Gerassimos A. , Prospathopoulos Aristides M.
Published: July 2002

In this work, a normal-mode solution is presented for the three-dimensional problem of acoustic scattering from a penetrable horizontally layered cylindrical obstacle in a shallow-water waveguide. The ocean environment around the obstacle is considered horizontally stratified and the bottom is assumed to be rigid. In the general case of depth-dependent sound-speed and density profiles (ssdp) the total acoustic field is calculated numerically, while an analytic solution is obtained in the special case of depth-independent ssdp. Numerical results concerning the transmission loss outside and inside single or double-layered cylindrical structures made of acoustic materials are given for a typical depth-dependent ocean environment. Comparisons with the cases of ideally soft and ideally hard cylindrical obstacles [J. Acoust. Soc. Am. 100, 206–218 (1996)] are also made, illustrating the effect of acoustic properties of the obstacle. An important feature, which clearly emerges from the theoretical analysis and the numerical results, is the necessity of including evanescent modes in the calculations, in order to obtain physically meaningful and numerically accurate results. Furthermore, analytical expressions for the scattering cross section of a (penetrable or impenetrable) cylindrical obstacle are derived in terms of the expansion coefficients of the pressure field, and their behavior as frequency increases is numerically investigated. The solution presented in this paper, although addressing a special geometry, provides a means for handling strong discontinuities in both vertical and horizontal directions, and can serve as a benchmark solution to a problem for which no general numerical model exists, i.e., modeling acoustic scattering from a 3D obstacle in a 3D shallow-water waveguide.
When is a ‘‘fuzzy’’ not a fuzzy (continued)?
Authors: Strasberg M.
Published: July 2002

The term ‘‘fuzzy substructures’’ as originally coined by C. Soize includes four categories of substructures whose influence on the vibratory behavior of the master structure to which they are attached may be significantly different. Either (1) the substructures are sufficiently numerous and their modal antiresonant frequencies sufficiently close to each other to result in modal overlap over the frequency range of interest; or (2) they do not have modal overlap; also, either (a) successive modal frequencies are separated by a constant frequency increment, or (b) the frequency increments are irregular. The effect of category (1) substructures on the master structure is independent of the detailed spacing between modal frequencies, provided modal overlap exists, for both steady-state and transient excitation. Contrariwise, the effect of category (2) substructures on the transient behavior of the master structure does depend on whether or not the modal frequencies are equally spaced. Although the statistical average behavior of an ensemble of such (2b) substructures may be similar to that of category (1), individual members of the ensemble may behave quite differently from their average. The differences will be exhibited by examples. To avoid confusion, it is suggested that the term ‘‘fuzzy structures’’ be limited to substructures with modal overlap
Response of gray whales to low-frequency sounds
Authors: Buck John R. , Tyack Peter L.
Published: July 2002

One transducer from the U.S. Navy SURTASS-LFA source was used during January 1998 to expose migrating gray whales off the California coast to low-frequency sound. These transmissions were 42 s in duration, repeating every 6 min, and 160–330 Hz. The whales were observed from shore stations north and south of the source location. Each pod of whales’ closest point of approach (CPA) to the sound source was estimated from the shore observations. The received level (RL) at the CPA was estimated using measured transmission loss curves and the known source level. The probability of observing whale pods at each RL is computed under both playback and control conditions. The difference between these probabilities as a function of RL provides a measure of avoidance for the animals. Previous work [Malme et al. (1984)] found a 50% change in these probabilities at a RL of 120 dB re:1μPa. For an inshore source location, the current work found 50% avoidance occurred at a RL of 141 dB, with 95% confidence bounds of ±3 dB derived by bootstrap statistical methods. For the offshore source location, 50% avoidance was not achieved for any observed RL. [Work supported by ONR.]
Mapping the regional variability of the California Current acoustically using a waveform inversion method
Authors: Han Sang-Kyu , Collins Curtis A. , Miller Christopher W. , Chiu Ching-Sang , Worcester Peter
Published: July 2002

To measure the large-scale variability in the California Current System, tomography signals are transmitted once every four days by a HLF-5 sound source moored on top of Hoke Seamount, approximately 600 km offshore from California. After propagating through the California Current Front and then upslope through inshore waters, the acoustic signals are recorded by a decommissioned SOSUS array off Point Sur. The processed time series shows four stable groups of arrivals that are consistently present in all of the transmissions. The fine structure within each group, however, varies from time to time. Using a ray-based range-dependent propagation model, with input sound speed field and bathymetry derived from hydrographic and echo sounding measurements, the arrival structure was simulated. Model results indicate that each of the four groups was composed of overlapping individual ray arrivals and that the variation of the fine structure within each group was due to phase interference. A waveform inversion scheme accounting for the multipath interference within each ray group is formulated. Using least-squares techniques, the scheme estimates the coefficients of one- or two-dimensional empirical orthogonal functions analyzed from the CalCOFI data. The inverse technique and results are presented and discussed. [Research supported by NOPP.]
Group delays of distortion product otoacoustic emissions: Relating delays measured with f1- and f2-sweep paradigms
Authors: Prijs Vera F. , Schneider Sandra , Schoonhoven Ruurd
Published: July 2002

A theoretical analysis is presented of group delays of distortion product otoacoustic emissions (DPOAEs) measured with the phase-gradient method. The aim of the analysis is to clarify the differences in group delays D1 and D2, obtained using the f1- and the f2-sweep paradigms, respectively, and the dependence of group delays on the order of the DPOAE. Two models are considered, the place-fixed and the wave-fixed models. While in the former model the generation place is assumed to be invariant with both f1- and f2-sweeps, in the latter model the shift of generation place is fully accounted for. By making a simple local approximation of the cochlear scale invariance, a mathematical conversion from phase-place to phase-frequency gradients is incorporated in the wave-fixed model. Under the assumption that the DPOAE (as recorded at the best f2/f1 ratio) is dominated by the contribution from the generation site and not by, e.g., reflection components, the analysis leads to simple expressions for the ratio and difference between D1 and D2. Validation of the models against experimental data indicates that lower sideband DPOAEs (2 f1−f2, 3f1−2 f2, 4f1−3f2) are most consistent with the wave-fixed model. Upper sideband components (2 f2−f1), in contrast, are not properly described by either the place-fixed or the wave-fixed model, independent whether DPOAE generation is assumed to originate at the f2 or at the more basally located fdp characteristic place.
Localization of amplitude-modulated high-frequency noise
Authors: Eberle Geoff , McAnally Ken I. , Martin Russell L. , Flanagan Patrick
Published: July 2002

This study investigated whether listeners can use interaural time differences (ITDs) in the amplitude envelope to localize high-frequency sounds in a free field. Localization accuracy was measured for high-frequency (7 to 14 kHz) noise with and without an imposed amplitude modulation (AM) at 20, 80 or 320 Hz. Only AM at 320 Hz led to more accurate localization relative to the nonmodulated condition. The results of a control experiment suggest that the improvement in localization accuracy was due to an increase in stimulus bandwidth, rather than the temporal cues provided by the modulation.
Frequency beamforming of dolphin whistles using a sparse three-element towed array
Authors: Thode Aaron , Norris Thomas , Barlow Jay
Published: July 2002

Acoustic bearings are obtained from dolphin whistles using frequency-domain (FD) beamforming techniques on signals recorded on a three-element 9-m aperture towed array. Due to the wide element separation, the high-frequency (kHz range) signals generate numerous grating lobes, but these lobes shift bearing with beamformed frequency, allowing identification of the true bearing whenever the whistles have over 1 kHz bandwidth. This method was validated by matching a sighting of a compact group of dolphins with acoustic bearing estimates. The system was subsequently used to detect and determine bearings from animals at least 3 km away and in Beaufort 5+ conditions. Frequency-domain beamforming has advantages over temporal cross correlation when the signals are faint and/or overlapping.
Oscillating reed valves—An experimental study
Authors: Tarnopolsky A. Z. , Fletcher N. H. , Lai J. C. S.
Published: July 2002

The results of experiments on the threshold behavior and large-amplitude oscillation of “outward-swinging door” vibrating flap valves in an air environment are reported and compared with the predictions of a simple nonlinear theory that parametrizes aerodynamic effects by means of a simple damping coefficient together with a contraction coefficient for the flow. The agreement is acceptably good for the threshold blowing pressure for valve oscillation, the large-signal vibration amplitude, the pressure jump in the transition from threshold to large-signal behavior, and the variation in vibration frequency, all as functions of reservoir volume. The calculated pressure waveform in the reservoir has the observed phase and magnitude but fails to reproduce finer details. It is concluded that the simple theory provides an adequate account of the behavior of such valves. There are just two parameters in the theory, describing jet contraction and aerodynamic damping, respectively. Since these may depend significantly upon the detailed geometry, valves with different shapes may behave in quantitatively different ways.
Binaural effects in center-frequency modulation detection interference for vowel formants
Authors: Lyzenga J. , Carlyon R. P.
Published: July 2002

The detection of slow (5 Hz) center-frequency modulations of formants (signals) can be impaired by the simultaneous presentation of off-frequency modulated formants (maskers) to the same ear [J. Lyzenga and R. P. Carlyon, J. Acoust. Soc. Am. 105, 2792–2806 (1999)]. In the present study we examine this “formant-frequency modulation detection interference (FMDI)” for various binaural masker presentation schemes. Signals and maskers were formantlike complex tones, centered around 1500 and 3000 Hz, respectively. Fundamentals of 80 and 240 Hz were used. The signals were presented to the right ear. The maskers were presented either to the right, the left, or to both ears, and they were either unmodulated or modulated at a slow rate (10 Hz). They had the same fundamental as the signals. Hardly any interference was found for the unmodulated maskers. For modulated maskers, the amount of FMDI depended strongly on the binaural masker presentation scheme. Substantial interference was found for the ipsilateral maskers. Interference was smaller for the contralateral maskers. In both cases the FMDI increased with increasing masker level. Substantial interference was also found for the binaural maskers. Imposing different interaural time and level differences (ITDs and ILDs) on maskers and signals did not affect FMDI. The same was true for the ITD condition when the maskers had different fundamentals than the signals, though FMDI was slightly smaller here. The amount of interference for the binaural maskers was roughly equal to that of the corresponding monaural masker with the largest effect. The data could not be described accurately using a model based on the loudness of the maskers. On the other hand, they were well described by a model in which the amount of FMDI was predicted from a “weighted combination” of the monaural masker levels.
Statistical Variability of Ultimate Properties of SBR Gum Vulcanizates
Authors: Fedors R. F. , Landel R. F.
Published: July 2002

The statistical variability of ultimate properties for 8 samples of SBR-sulfur gum vulcanizates differing in crosslink density by a factor of about 25 was studied. It is shown that these variability data, determined at one rate and one temperature, can be correlated when plotted as a reduced failure envelope. The envelope obtained in this manner agrees reasonably well with the reduced envelope previously reported which was constructed from break data obtained by testing (a) single specimens of constant crosslink density at varying rate and temperature and (b) single specimens at constant rate and temperature but varying crosslink density. It is also shown that the statistical variability data for all samples, including a benzene-soluble one, can be represented by a double exponential cumulative distribution function. It is also shown, in agreement with previous work, that the most probable values of σb when plotted as a function of νe exhibit a maximum in σb at a low value of νe.
Experimental Determination of the Secondary Normal Stress Difference for Aqueous Polymer Solutions
Authors: Huppler John D.
Published: July 2002

An axial annular flow device has been utilised to determine the secondary normal stress difference τ22−τ33 [where the velocity field is v1=v1(x2)] for several aqueous polymer solutions. Data are presented on the radial pressure difference, at a fixed axial position, between inner and outer walls of the annulus vs. the axial pressure gradient. The data are analyzed by numerically integrating the radial component of the equation of motion using a nonlinear generalized Maxwell model proposed by Spriggs to obtain a trial function for τ22−τ33. Results indicate that the secondary normal stress difference, while not zero, is considerably smaller than the primary normal stress difference, τ11−τ33, for the solutions studied.
Rheological Study on Cold and Warm Processings of Polycarbonate
Authors: Ueno Shoichi , Yamazaki Hiroaki , Oue Takeshi , Ito Katsuhiko , Tsutsui Makoto
Published: July 2002

The retentivity of shape in uniaxial compression of polycarbonate resin when processing in the cold and warm processing temperature range was investigated experimentally. Iupilon, a polycarbonate resin manufactured by the solvent process, was used as the sample. Strain recovery of test specimens, which were processed by compression at various temperatures, was measured after free annealing by raising the temperature gradually to a temperature higher than the processing temperature. Polycarbonate has superior processability in the vicinity of room temperature and has good strain-freezing properties at temperatures below the glass transition temperature; however, strain is recovered completely at temperatures above the glass transition point. A new Erichsen testing apparatus was developed for measuring the temperature dependence of processability of sheet in the cold and warm temperature range. A punch is pushed into the sheet whose temperature has been made uniform in a constant temperature apparatus at a fixed stroke speed; the Erichsen depth at fracture at the various temperatures is measured. Results indicated that processability of polycarbonate sheet (thickness, 1 mm) improves gradually with temperature rise as high as the glass transition point. Experiments on strain recovery of an Erichsen test specimen were carried out in the same manner as in the case of uniaxial compression. The results for combined stresses, such as in Erichsen bulging, were similar to those of uniaxial compression. An attempt is being made to utilize such Erichsen bulging test specimens for environmental stress cracking tests of polycarbonate.
Stress-Birefringent Patterns of a Viscoelastic Fluid at a Sharp-Edged Entrance
Authors: Fields T. R. , Bogue D. C.
Published: July 2002

Stress-birefringent patterns were determined for a viscoelastic fluid (14 wt-% polystyrene in Aroclor) flowing into a sharp-edged channel entrance. The final data are point-by-point shear stresses and differences in normal stresses. Independent shear and normal stress data were obtained on the Weissenberg Rheogoniometer. In developed straight channel flow, the experimental shear stresses are in quantitative agreement with those calculated from the rheogoniometer data; the normal stresses are of the correct magnitude but the agreement is not quantitative. Very good detail of the stresses at the corners and in the entrance region is available. The entrance regions are of the order of one large channel width upstream and one small channel width downstream, as judged by the approach of the stresses to within a few per cent of their developed values. The accelerating region upstream of the entrance was treated theoretically with a simplified version of the theory of Bernstein, Kearsley, and Zapas, using the model of radial, plug flow. Although a reasonably good prediction of the normal stresses along the centerline is obtained, the predominance of the Newtonian term does not make the check a sensitive one.
Nonlinear Stability of Plane Poiseuille Flow of Viscoelastic Liquids
Authors: Porteous K. C. , Denn M. M.
Published: July 2002

The stability of plane Poiseuille flow to finite disturbances was studied for the second order fluid using the cascade (Stuart-Watson-Reynolds-Potter) method. The analysis was carried out for elasticity numbers up to 10−4. In this range the Deborah number based upon disturbance propagation is small and the second order fluid is a consistent constitutive approximation. In contrast to linear theory in this region, elasticity has a stabilizing effect on finite disturbances relative to the Newtonian liquid and the difference between stability behavior of Newtonian and slightly elastic liquids tends to disappear.
Constitutive Equations for Dilute Polymer Solutions
Authors: James David F.
Published: July 2002

The theories of continuum mechanics and molecular physics are brought together to provide constitutive relations for dilute polymer solutions. The required compatibility shows that the stress tensor is composed of a sum of stress tensors, each satisfying Oldroyd's differential constitutive equation. In each equation, the higher order strain rate terms are not retained, and the five material constants are found solely by utilizing results from Rouse's molecular theory. When the fluid acceleration is small, it is shown that the set of constitutive relations may be approximated by a single equation of the Oldroyd type, containing only two material constants.
A Critical Test for a Class of Nonlinear Constitutive Equations
Authors: Van Es H. E. , Christensen R. M.
Published: July 2002

Recently Yamamoto proposed a new procedure to determine the relevant material properties for a widely used viscoelastic fluid constitutive relation. The procedure, based on a hypothetical dependence of the memory function on the rate of deformation, is rather complicated and introduces a few approximations. Also, the procedure was not actually applied to a particular set of experimental data. In this paper it is shown how the basic hypothesis of the constitutive equation can be tested quickly and simply, without introducing any approximations, and in fact without directly determining the relevant memory function. This new procedure is applied to one of the standard model materials; the constitutive relation is revealed to be an inadequate formation for this material.
Velocity Lag, Axial Thrust, and Edge Effects in The Eccentric Disc Rheometer
Authors: Payvar Parviz , Tanner R. I.
Published: July 2002

Velocity lag between the two discs in the eccentric disc rheometer is determined analytically for a Newtonian fluid, the second order fluid, and for general simple fluids when the offset and slip are small. It is established that the normal thrust between the discs does not measure the second normal stress difference. Experimental measurements of the velocity lag are in good agreement with the analytical expressions which are developed. The influence of the velocity lag on the forces exerted on the free disc is predicted. Experimental results with two different edge geometries indicate the strong influence of edge effects on the forces exerted on the free disc. The correct relationship between the fluid viscosity and the measured forces, therefore, may require detailed analysis of the flow situation in the edge region or careful experimental extrapolation procedures.
Transient Normal Stress Measurement
Authors: Chang K. I. , Yoo S. S. , Hartnett J. P.
Published: July 2002

For the critical evaluation of the rheological equations of state for polymer solutions, steady-state and dynamic experiments including transient normal and shear stress measurements are required. It has been found that the normal force measurement system in the Weissenberg Rheogoniometer (WRG) is not suitable for the transient normal stress measurement. Therefore, the leaf spring in the WRG was replaced by one of a set of cantilevers with various rigidities, and the servo system was discarded. The present investigation reveals that the transient normal stress data depend on the rigidity of the cantilevers used. Thus, a series of normal stress measurements with several cantilevers was made to obtain reliable data. The results show that the normal forces in the transient experiments approach asymptotic values as the cantilever rigidity increases. Therefore, these asymptotic values were taken as representative of the material response. The present study indicates that a forced damped vibration mechanism may be responsible for the systematic dependence of the transient normal forces on the cantilever rigidity. Furthermore, the shear stress response of glycerin under a suddenly started shear flow suggests that the undershoot commonly observed in the stress growth experiment may be an apparatus response rather than a material property.
Processability Difference of Elastomers Observed by Rate Dependence of Viscoelastic Properties
Authors: Nakajima N. , Poh H. S. , Kumler P. R. , Collins E. A.
Published: July 2002

Two similar elastomers of known difference in processability are examined by means of the MTS high speed tensile tester and the Mooney rheometer at a low speed. The samples are butadiene-acrylonitrile copolymers having 42% acrylonitrile content. Measurements on the MTS tester are made at −35, 24, and 85°C and cross-head speeds of 2.5, 25, and 250 in./sec. These speeds correspond to strain rates of 468, 4680, and 46,800%/sec, respectively. In addition, measurements are made at 100°C and 2.5 in./sec. A Mooney rheometer is used to obtain shear stress-strain curves at 100°C and 0.05 rpm. Both tensile and shear stress-strain curves are used to construct master curves, which cover 17 decades of the deformation rate. A major difference between the samples is found in the low rate range of the observation. The ultimate properties are also examined. Rather small sample-to-sample differences are observed in the stresses at break.
On the Stability of Flow in Channels with a Moving Boundary: The Mold Filling Problem
Authors: Mhaskar R. D. , Shah Y. T. , Pearson J. R. A.
Published: July 2002

A linearized stability theory for the flow of a hot fluid in a cold channel is adapted here to the case of a moving boundary characteristic of injection molding of thermoplastics. The predictions for instability fall within expected experimental limits and two photographs show experimental evidence of a phenomenon that may arise in the manner predicted by the analysis.
X-ray powder diffraction data and Rietveld refinement for a new iodate: (LiFe1/3)(IO3)2
Authors: Lan Y. C. , Chen X. L. , Tao Z. , Xie A. Y. , Jiang P. Z. , Xu T. , Xu Y. P.
Published: July 2002

The structure of a new iodate, (LiFe1/3)(IO3)2, has been determined. The new compound has a hexagonal structure with the lattice parameters a=5.4632(2) Å, c=5.0895(6) Å, Z=1. The density is 4.70 g cm−3. Rietveld refinement confirms that the compound has a space group of P63 (173). Fe and Li atoms randomly distribute on the 2a cation site.
Nonpharmacological Interventions to Lengthen Sleep Duration in Healthy Children
Authors: Magee Lucia , Goldsmith Lucy P. , Chaudhry Umar A. R. , Donin Angela S. , Wahlich Charlotte , Stovold Elizabeth , Nightingale Claire M. , Rudnicka Alicja R. , Owen Christopher G.
Published: September 2022

Importance

Adequate sleep duration is necessary for many aspects of child health, development, and well-being, yet sleep durations for children are declining, and effective strategies to increase sleep in healthy children remain to be elucidated.

Objective

To determine whether nonpharmaceutical interventions to improve sleep duration in healthy children are effective and to identify the key components of these interventions.

Data Sources

CENTRAL, MEDLINE, Embase, PsycINFO, Web of Science Core collection, ClinicalTrials.gov, and WHO trials databases were searched from inception to November 15, 2021.

Study Selection

Randomized clinical trials of interventions to improve sleep duration in healthy children were independently screened by 2 researchers. A total of 28 478 studies were identified.

Data Extraction and Synthesis

Data were processed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) reporting guideline. Random-effects meta-analytic models were used to estimate pooled effect sizes.

Main Outcomes and Measures

Difference in sleep duration, measured in minutes.

Results

A total of 13 539 child participants from 45 randomized clinical trials were included. Of these, 6897 (50.9%) were in the intervention group and 6642 (49.1%) in the control group, and the mean age ranged from 18 months to 19 years. Pooled results indicate that sleep interventions were associated with 10.5 minutes (95% CI, 5.6-15.4) longer nocturnal sleep duration. There was substantial variation between trials. Sources of variation that were not associated with the study effect size included age group, whether the population was identified as having a sleep problem or being at a socioeconomic disadvantage (eg, coming from a low-income family or area), method of assessment of sleep duration (objective vs subjective), location of intervention delivery (home vs school), whether interventions were delivered in person or used parental involvement, whether behavioral theory was used, environmental change, or had greater or lower intensity. Interventions that included earlier bedtimes were associated with a 47-minute sleep extension (95% CI, 18.9-75.0; 3 trials) compared with remaining studies (7.4 minutes; 95% CI, 2.9-11.8; 42 trials) (P = .006 for group difference). Trials of shorter duration (6 months or less) had larger effects.

Conclusions and Relevance

Interventions focused on earlier bedtimes may offer a simple, pragmatic, effective way to meaningfully increase sleep duration that could have important benefits for child health.
Single‐Cell Transcriptomic Census of Endothelial Changes Induced by Matrix Stiffness and the Association with Atherosclerosis
Authors: Zamani Maedeh , Cheng Yu‐Hao , Charbonier Frank , Gupta Vivek Kumar , Mayer Aaron T. , Trevino Alexandro E. , Quertermous Thomas , Chaudhuri Ovijit , Cahan Patrick , Huang Ngan F.
Published: September 2022

Vascular endothelial cell (EC) plasticity plays a critical role in the progression of atherosclerosis by giving rise to mesenchymal phenotypes in the plaque lesion. Despite the evidence for arterial stiffening as a major contributor to atherosclerosis, the complex interplay among atherogenic stimuli in vivo has hindered attempts to determine the effects of extracellular matrix (ECM) stiffness on endothelial‐mesenchymal transition (EndMT). To study the regulatory effects of ECM stiffness on EndMT, an in vitro model is developed in which human coronary artery ECs are cultured on physiological or pathological stiffness substrates. Leveraging single‐cell RNA sequencing, cell clusters with mesenchymal transcriptional features are identified to be more prevalent on pathological substrates than physiological substrates. Trajectory inference analyses reveal a novel mesenchymal‐to‐endothelial reverse transition, which is blocked by pathological stiffness substrates, in addition to the expected EndMT trajectory. ECs pushed to a mesenchymal character by pathological stiffness substrates are enriched in transcriptional signatures of atherosclerotic ECs from human and murine plaques. This study characterizes at single‐cell resolution the transcriptional programs that underpin EC plasticity in both physiological or pathological milieus, and thus serves as a valuable resource for more precisely defining EndMT and the transcriptional programs contributing to atherosclerosis.
Highly Conductive and Underwater Stable Ionic Skin for All‐Day Epidermal Biopotential Monitoring
Authors: Chen Tinglei , Ye Guo , Wu Haowei , Qi Shuyan , Ma Guorong , Zhang Yan , Zhao Yan , Zhu Jia , Gu Xiaodan , Liu Nan
Published: September 2022

Epidermal biopotential monitoring is an essential part of wearable healthcare. For 24 × 7 h detection of electrophysiological signals, commercialized gel electrodes cannot satisfy the demands, in particular for monitoring in humidity or underwater. Epidermal electrodes that can be stable and operated underwater are required. Here, a highly conductive and optically camouflaged ionic skin for epidermal biopotential monitoring under aquatic circumstances is designed. There is a fluorine‐dipole interaction system consisting of fluorine‐rich segment in the polyurethane backbone and fluorine‐cation bonded 1‐ethyl‐3‐methylimidazolium bis(trifluoromethyl‐sulfonyl) imide ([EMIM]+ [TFSI]−) ion pairs distributed in the polymer matrix. Benefitting from the fluorine‐cation interaction, the ionic skin gains remarkable ionic conductivity (1.04 × 10−3 S cm−1), high optical transmittance (92%), and improved mechanical strength (3.1 MPa of Young's modulus). Via cations caught by fluorine‐rich segments, its ionic conductivity can keep stable even by rinsing or fierce washing in water. The epidermal electrode based on such ionic skin can accurately measure a variety of electrophysiological signals undboth atmospheric and aquatic environments, exhibiting robust and excellent signal quality. As the first demonstration of ionic skin‐based electrophysiological electrodes, the ionic skin paves a new way for all‐day wearable healthcare.
Developing Thermoregulatory Hydrogel Electrolyte to Overcome Thermal Runaway in Zinc‐Ion Batteries
Authors: Meng Yuan , Zhang Lifang , Peng Mingji , Shen Danni , Zhu Changhao , Qian Siyi , Liu Jie , Cao Yufeng , Yan Chenglin , Zhou Jinqiu , Qian Tao
Published: September 2022

Zinc‐ion batteries (ZIBs) that use water‐based electrolytes have attracted significant attention. However, under harsh conditions, extreme heat is accumulated inside ZIBs, which inevitably causes thermal runway risk. Therefore, the practical applications of rechargeable ZIBs are significantly limited because the internal heat accumulated by harsh conditions induces drastic bulges or even explosions. To overcome this limitation, a self‐adaptive thermoregulatory hydrogel electrolyte (TRHE) that integrates phase transition chains with endothermic effects into agarose backbones via hydrogen bonding interactions is reported. Under extreme conditions, TRHE can tolerate sudden thermal shock; thus, ZIBs can function properly for a period in environments (100 °C) owing to their thermally self‐regulating feature, which alleviates the thermal issues associated with batteries. The hydrogel network with uniform ion migration channels can accelerate ion transport and homogenize ion distribution to realize dendrite inhibition; in addition, other pressing concerns can be effectively resolved, including hydrogen evolution and Zn corrosion, which significantly contribute to the outstanding electrochemical performance. It is believed that the proposed TRHE will help in overcoming thermal runaway in ZIBs and in other aqueous batteries.
Confinement‐Driven Inverse Domain Scaling in Polycrystalline ErMnO3
Authors: Schultheiß Jan , Xue Fei , Roede Erik , Ånes Håkon W. , Danmo Frida H. , Selbach Sverre M. , Chen Long‐Qing , Meier Dennis
Published: September 2022

The research on topological phenomena in ferroelectric materials has revolutionized the way people understand polar order. Intriguing examples are polar skyrmions, vortex/anti‐vortex structures, and ferroelectric incommensurabilties, which promote emergent physical properties ranging from electric‐field‐controllable chirality to negative capacitance effects. Here, the impact of topologically protected vortices on the domain formation in improper ferroelectric ErMnO3 polycrystals is studied, demonstrating inverted domain scaling behavior compared to classical ferroelectrics. It is observed that as the grain size increases, smaller domains are formed. Phase field simulations reveal that elastic strain fields drive the annihilation of vortex/anti‐vortex pairs within the grains and individual vortices at the grain boundaries. The inversion of the domain scaling behavior has far‐reaching implications, providing fundamentally new opportunities for topology‐based domain engineering and the tuning of the electromechanical and dielectric performance of ferroelectrics in general.
Resistive Switching Crossbar Arrays Based on Layered Materials
Authors: Lanza Mario , Hui Fei , Wen Chao , Ferrari Andrea C.
Published: September 2022

Resistive switching (RS) devices are metal/insulator/metal cells that can change their electrical resistance when electrical stimuli are applied between the electrodes, and they can be used to store and compute data. Planar crossbar arrays of RS devices can offer a high integration density (>108 devices mm−2) and this can be further enhanced by stacking them three‐dimensionally. The advantage of using layered materials (LMs) in RS devices compared to traditional phase‐change materials and metal oxides is that their electrical properties can be adjusted with a higher precision. Here, the key figures‐of‐merit and procedures to implement LM‐based RS devices are defined. LM‐based RS devices fabricated using methods compatible with industry are identified and discussed. The focus is on small devices (size < 9 µm2) arranged in crossbar structures, since larger devices may be affected by artifacts, such as grain boundaries and flake junctions. How to enhance device performance, so to accelerate the development of this technology, is also discussed.
A Smart Photothermal Nanosystem with an Intrinsic Temperature‐Control Mechanism for Thermostatic Treatment of Bacterial Infections
Authors: Wang Jiaxin , Hao Boyi , Xue Ke , Fu Hao , Xiao Minghui , Zhang Yongxin , Shi Linqi , Zhu Chunlei
Published: September 2022

Photothermal therapy (PTT) has attracted extensive attention in disease treatments. However, conventional photothermal systems do not possess a temperature‐control mechanism, which poses a serious risk to healthy tissues and/or organs due to inevitable thermal damage. Herein, a smart photothermal nanosystem with an intrinsic temperature‐control mechanism for thermostatic treatment of bacterial infections is reported. The smart photothermal nanosystem is constructed by loading a thermochromic material into a hollow‐structured silica nanocarrier, in which the thermochromic material is composed of naturally occurring phase‐change materials (PCMs), a proton‐responsive spirolactone, and a proton source. The resulting nanosystem shows strong near‐infrared (NIR) absorption and efficient photothermal conversion in solid PCMs but becomes NIR‐transparent when PCMs are melted upon NIR irradiation. Such an attractive feature can precisely regulate the photothermal equilibrium temperature to the melting point of PCMs, regardless of the variation in external experimental parameters. In contrast to conventional PTT with severe thermal damage, the reported smart photothermal nanosystem provides an internal protection mechanism on healthy tissues and/or organs, which remarkably accelerates the recovery of bacteria‐infected wounds. The smart photothermal nanosystem is a versatile PTT platform, holding great promise in the safe and efficient treatment of bacterial infections and multimodality synergistic therapy.
Dual‐Cascade Responsive Nanoparticles Enhance Pancreatic Cancer Therapy by Eliminating Tumor‐Resident Intracellular Bacteria
Authors: Kang Xiaoxu , Bu Fanqiang , Feng Wenli , Liu Fang , Yang Xuankun , Li Haofei , Yu Yingjie , Li Guofeng , Xiao Haihua , Wang Xing
Published: September 2022

The limited drug penetration and robust bacteria‐mediated drug inactivation in pancreatic cancer result in the failure of chemotherapy. To fight against these issues, a dual‐cascade responsive nanoparticle (sNP@G/IR) that can sequentially trigger deep penetration, killing of intratumor bacteria, and controlled release of chemo‐drug, is reported. sNP@G/IR consists of a hyaluronic acid (HA) shell and glutathione (GSH)‐responsive polymer‐core (NP@G/IR), that encapsulates gemcitabine (Gem) and photothermal agent (IR1048). The polymer core, as an antibiotic alternative, is tailored to exert optimal antibacterial activity and selectivity. sNP@G/IR actively homes in on the tumor due to the CD44 targeting of the HA shell, which is subsequently degraded by the hyaluronidase in the extracellular matrix. The resultant NP@G/IR in decreased size and reversed charge facilitates deep tumor penetration. After cellular endocytosis, the exposed guanidine on NP@G/IR kills intracellular bacteria through disrupting cell membranes. Intracellular GSH further triggers the controlled release of the cargo. Thus, the protected Gem eventually induces cell apoptosis. Under laser irradiation, the hyperthermia of IR1048 helps further elimination of tumors and bacteria. Moreover, sNP@G/IR activates immune response, thereby reinforcing anticancer capacity. Therefore, this dual‐cascade responsive sNP@G/IR eliminates tumor‐resident intracellular bacteria and augments drug delivery efficacy, providing a new avenue for improving cancer therapy.
Engineering of Covalent Organic Framework‐Based Advanced Platforms for Enzyme Immobilization: Strategies, Research Progress, and Prospects
Authors: Wang Shizhao , Xia Xiaocong , Chen Fen‐Er
Published: September 2022

Driven by green and sustainable methodologies for chemical manufacturing, enzymes are forecast to have much to prospect in the coming years due to their high activity and selectivity. However, the fragile active spatial‐conformation of an enzyme is predominantly maintained by weak intermolecular interactions, showing quite sensitive to thermal, pH, and chemical chemoreception. Thus, the low activity and recyclability result from structural instability can hardly meet the prototype of green chemistry in commercial process. Covalent organic frameworks (COFs) are stable extended porous network materials assembled by organic linkers in a moderate way. Due to their pre‐designable structures, an enzyme possesses the access to be immobilized to the interior or surface of COF skeletons via covalent or noncovalent processes, which can afford protection to enzymes in harsh conditions. Moreover, with the improved stability and cyclicity, the formed COF/enzyme biocomposites can facilitate broader horizon. Herein, this review mainly canvasses the advances in the emerging field of COF/enzyme biocomposites, sketching the factors that are critical in building COF/enzyme systems and the applications of registered enzyme host platforms reported in recent years.