bluuebunny/crossref_metadata_2025 huggingface dataset:
Chord distributions across 3D digital images of a human thoracic vertebra
Authors: Jokisch D. W. , Patton P. W. , Rajon D. A. , Inglis B. A. , Bolch W. E.
Published: July 2002

Radiation dose estimates to the trabecular region of the skeleton are of primary importance due to recent advancements in nuclear medicine. Establishing methods for accurately calculating dose in these regions is difficult due to the complex microstructure of this anatomic site and the typical ranges of beta‐particles in both bone and marrow tissues. At the present time, models of skeletal dosimetry used in clinical medicine rely upon measured distributions of straight‐line path lengths (chord lengths) through bone and marrow regions. This work develops a new three‐dimensional, digital method for acquiring these distributions within voxelized images. In addition, the study details the characteristics of measuring chord distributions within digital images and provides a methodology for avoiding undesirable pixel or voxel effects. The improved methodology has been applied to a digital image (acquired via NMR microscopy) of the trabecular region of a human thoracic vertebra. The resulting chord‐length distributions across both bone trabeculae and bone marrow cavities were found to be in general agreement with those measured in other studies utilizing different methods. In addition, this study identified that bone and marrow space chord‐length distributions are not statistically independent, a condition implicitly assumed within all current skeletal dosimetry models of electron transport. The study concludes that the use of NMR microscopy combined with the digital measurement techniques should be used to further expand the existing Reference Man database of trabecular chord distributions to permit the development of skeletal dosimetry models which are more age and gender specific.
Influence of electron contamination on in vivo surface dosimetry for high‐energy photon beams
Authors: Sjögren Rickard , Karlsson Mikael
Published: July 2002

The influence of the electron contamination at in vivo dosimetry with diodes on the patient surface has been investigated by introducing different accessories in the beam path and by changing the field size and SSD. The results show a clear correlation between the electron contamination at an effective measuring depth of the diode and the signal from the patient diode. When the electron contamination is taken into account the agreement between the diode values and the absorbed dose is greatly improved. More accurate in vivo dosimetry with less error margins is therefore possible if better predictions of the electron contamination in high‐energy photon beams can be performed.
Air‐cooling of direct‐coupled ultrasound applicators for interstitial hyperthermia and thermal coagulation
Authors: Deardorff Dana L. , Diederich Chris J. , Nau William H.
Published: July 2002

The feasibility of using air‐cooling to improve the thermal penetration of direct‐coupled interstitial ultrasound (US) applicators was investigated using biothermal simulations, bench experiments, phantom testing, and in vivo thermal dosimetry. Two applicator configurations using tubular US transducers were constructed and tested. The first design, intended for simultaneous thermobrachytherapy, utilizes a 2.5 mm OD transducer with a central lumen to accommodate a radiation source from remote afterloaders. The second applicator consists of a 2.2 mm OD transducer designed for coagulative thermal therapy. Both designs provide cooling of the inner transducer surface by the counterflow of chilled air or gas through the annulus of the enclosed applicator. The average convective heat transfer associated with each applicator was determined empirically from curve‐fits of radial steady‐state temperatures measured in a tissue‐mimicking phantom. High levels of convective heat transfer were demonstrated in both designs at relatively low flow rates Transient and steady‐state radial heating profiles were also measured in vivo (pig thigh muscle) with and without cooling. The therapeutic radius for hyperthermia (41–45 °C) was extended from 5–6 mm (without cooling) to 11–19 mm with air‐cooling (4.8 L min−1, airflow 10 °C), effectively doubling and tripling the thermal penetration in vivo. Similar improvements were demonstrated at higher temperatures with the thermal coagulation applicator. Biothermal simulations, which modeled the physical, thermal, and acoustic parameters of the air‐cooled applicator and surrounding tissue, were also used to investigate potential improvements in heating patterns. The simulated radial heating profiles with transducer cooling demonstrated significantly enhanced thermal penetration over the experimental range of convective transfer, and also agreed with in vivo results. These theoretical and experimental results clearly show air‐cooling controls the transducer surface temperature, significantly increases thermal penetration, and produces a greater treatment volume for direct‐coupled US applicators in hyperthermia and thermal coagulation.
Estimation of the noisy component of anatomical backgrounds
Authors: Bochud François O. , Valley Jean‐François , Verdun Francis R. , Hessler Christian , Schnyder Pierre
Published: July 2002

The knowledge of the relationship that links radiation dose and image quality is a prerequisite to any optimization of medical diagnostic radiology. Image quality depends, on the one hand, on the physical parameters such as contrast, resolution, and noise, and on the other hand, on characteristics of the observer that assesses the image. While the role of contrast and resolution is precisely defined and recognized, the influence of image noise is not yet fully understood. Its measurement is often based on imaging uniform test objects, even though real images contain anatomical backgrounds whose statistical nature is much different from test objects used to assess system noise. The goal of this study was to demonstrate the importance of variations in background anatomy by quantifying its effect on a series of detection tasks. Several types of mammographic backgrounds and signals were examined by psychophysical experiments in a two‐alternative forced‐choice detection task. According to hypotheses concerning the strategy used by the human observers, their signal to noise ratio was determined. This variable was also computed for a mathematical model based on the statistical decision theory. By comparing theoretical model and experimental results, the way that anatomical structure is perceived has been analyzed. Experiments showed that the observer's behavior was highly dependent upon both system noise and the anatomical background. The anatomy partly acts as a signal recognizable as such and partly as a pure noise that disturbs the detection process. This dual nature of the anatomy is quantified. It is shown that its effect varies according to its amplitude and the profile of the object being detected. The importance of the noisy part of the anatomy is, in some situations, much greater than the system noise. Hence, reducing the system noise by increasing the dose will not improve task performance. This observation indicates that the tradeoff between dose and image quality might be optimized by accepting a higher system noise. This could lead to a better resolution, more contrast, or less dose.
Illustrative example of Feynman’s rest of the universe
Authors: Han D. , Kim Y. S. , Noz Marilyn E.
Published: July 2002

Coupled harmonic oscillators occupy an important place in physics teaching. It is shown that they can be used for illustrating an increase in entropy caused by limitations in measurement. In the system of coupled oscillators, it is possible to make the measurement on one oscillator while averaging over the degrees of freedom of the other oscillator without measuring them. It is shown that such a calculation would yield an increased entropy in the observable oscillator. This example provides a clarification of Feynman’s rest of the universe.
Vocalization-correlated respiratory movements in the squirrel monkey
Authors: Häusler Udo
Published: July 2002

Respiratory abdominal movements associated with vocalization were recorded in awake squirrel monkeys. Several call types, such as peeping, trilling, cackling, and err-chucks, were accompanied by large vocalization-correlated respiratory movements (VCRM) that started before vocalization. During purring, in contrast, only small VCRM were recorded that started later after vocal onset. VCRM during trill calls, a vocalization type with repetitive frequency modulation, showed a modulation in the rhythm of the frequency changes. A correlation with amplitude modulation was also present, but more variable. As high frequencies need a higher lung pressure for production than low frequencies, the modulation of VCRM seems to serve to optimize the lung pressure in relation to the vocalization frequency. The modulation, furthermore, may act as a mechanism to produce different trill variants. During err-chucks and staccato peeps, which show a large amplitude modulation, a nonmodulated VCRM occurred. This indicates the existence of a laryngeal amplitude-controlling mechanism that is independent from respiration.
Second-harmonic generation in a sound beam reflected and transmitted at a curved interface
Authors: Makin Inder Raj S. , Averkiou Michalakis A. , Hamilton Mark F.
Published: July 2002

This article presents a model for second-harmonic generation in a sound beam that is reflected from or transmitted through a curved interface. Propagation in homogeneous fluids is assumed. Simple analytic solutions are derived for the case of focused Gaussian beams. The solutions are used to illustrate the effects of focusing or defocusing due to curvature of the interface, in combination with impedance change at the interface, on energy transfer from the fundamental to the second harmonic.
Dynamic measurements of the thermal dissipation function of reticulated vitreous carbon
Authors: Wilen L. A.
Published: July 2002

A volume modulation technique is employed to measure the complex compressibility of a gas in reticulated vitreous carbon (RVC). The complex compressibility depends on the geometry-dependent thermal coupling between the gas and the solid walls, and is related to the thermoacoustic function fκ, or equivalently F(λT). By measuring samples of different cross section and length, all external boundary effects are eliminated, so that F(λT) corresponding to bulk RVC is determined. Working down to very low frequencies achieves a wide range of values for the ratio of the thermal penetration depth to the mean pore size. As a test of the concept of “capillary-based porous media,” the results are compared to analytical solutions for F(λT) in circular, parallel plate and pin-array geometries. Measurements made at peak-to-peak gas displacement amplitudes exceeding the pore size in at least half of the sample showed no observable deviation from the small-amplitude results.
Transient response of an acoustic medium by an excited submerged spherical shell
Authors: Zakout U.
Published: July 2002

An exact closed-form solution is obtained for the transient response of an acoustic fluid due to an excited submerged spherical shell. Step axisymmetric stress acting on the inner surface of the shell is expanded into modal Fourier components in which for each modal stress systematic exact expressions for modal radial displacement of the shell, fluid pressure, fluid particle velocity and displacement are presented. The superiority of the formulations herein is its applicability to any time and spatial distance in the fluid as well as on the shell. The formulation also does not require additional numerical computations associated with other methods.
Finite-element method to study harmonic aeroacoustics problems
Authors: Peyret C. , Élias G.
Published: July 2002

The analysis of aeroacoustics propagation is required to solve many practical problems. As an alternative to Euler’s linearized equations, an equation was established by Galbrun in 1931. It assumes the flow verifies Euler’s equations and the perturbation is small and adiabatic. It is a linear second-order vectorial equation based on the displacement. Galbrun’s equation derives from a Lagrangian density and provides conservative expressions of the aeroacoustics intensity and energy density. A (CAA) method dealing with the numerical resolution of Galbrun’s equation using the finite-element method (FEM) is presented. The exact solution for the propagation of acoustic modes inside an axisymmetric straight-lined duct in the presence of a shear flow is known and compared with the FEM solution. Comparisons are found to be in good agreement and validate a first step in the development of a CAA method based on the FEM and Galbrun’s equation. The FEM is then applied to an axisymmetric duct including a varying cross section and a nonuniform flow with respect to both the axial and the radial coordinates. The expression of the aeroacoustics intensity implemented in the FEM provides an accurate in-duct power balance.
Numerical analysis of ultrasonic transmission and absorption of oblique plane waves through the human skull
Authors: Hayner Mark , Hynynen Kullervo
Published: July 2002

Ultrasonic transmission and absorption of oblique plane waves through the human skull are analyzed numerically for frequencies ranging from 1/2 to 1 MHz. These frequencies are optimum for noninvasive ultrasound therapy of brain disorders where numerical predictions of skull transmission are used to set the phase and amplitude of source elements in the phased array focusing system. The idealized model of the skull is a three-layer solid with ivory outer and inner layers and a middle marrow layer. Each layer is modeled as a flat, homogeneous, isotropic, linear solid with effective complex wave speeds to account for focused energy losses due to material damping and scattering. The model is used to predict the amplitude and phase of the transmitted wave and volumetric absorption. Results are reported for three different skull thicknesses: 3 mm, 6 mm, and 9 mm. Thickness resonances are observed in the transmitted wave for 3 mm skulls at all frequencies and for the 6 mm skulls below 0.75 MHz. Otherwise, the transmission is dominated by the direct wave. Skull phase errors due to shear waves are shown to minimally degrade the power at the focus for angles of incidence up to 20° from normal even for low material damping. The location of the peak volumetric absorption occurs either in the outer ivory or middle marrow layer and shown to vary due to wave interference.
A comparison of material classification techniques for ultrasound inverse imaging
Authors: Zhang Xiaodong , Broschat Shira L. , Flynn Patrick J.
Published: July 2002

The conjugate gradient method with edge preserving regularization (CGEP) is applied to the ultrasound inverse scattering problem for the early detection of breast tumors. To accelerate image reconstruction, several different pattern classification schemes are introduced into the CGEP algorithm. These classification techniques are compared for a full-sized, two-dimensional breast model. One of these techniques uses two parameters, the sound speed and attenuation, simultaneously to perform classification based on a Bayesian classifier and is called bivariate material classification (BMC). The other two techniques, presented in earlier work, are univariate material classification (UMC) and neural network (NN) classification. BMC is an extension of UMC, the latter using attenuation alone to perform classification, and NN classification uses a neural network. Both noiseless and noisy cases are considered. For the noiseless case, numerical simulations show that the CGEP–BMC method requires 40% fewer iterations than the CGEP method, and the CGEP–NN method requires 55% fewer. The CGEP–BMC and CGEP–NN methods yield more accurate reconstructions than the CGEP method. A quantitative comparison of the CGEP–BMC, CGEP–NN, and GN–UMC methods shows that the CGEP–BMC and CGEP–NN methods are more robust to noise than the GN–UMC method, while all three are similar in computational complexity.
Identification of complex stiffness tensor from waveform reconstruction
Authors: Leymarie N. , Aristégui C. , Audoin B. , Baste S.
Published: July 2002

An inverse method is proposed in order to determine the viscoelastic properties of composite-material plates from the plane-wave transmitted acoustic field. Analytical formulations of both the plate transmission coefficient and its first and second derivatives are established, and included in a two-step inversion scheme. Two objective functions to be minimized are then designed by considering the well-known maximum-likelihood principle and by using an analytic signal formulation. Through these innovative objective functions, the robustness of the inversion process against high level of noise in waveforms is improved and the method can be applied to a very thin specimen. The suitability of the inversion process for viscoelastic property identification is demonstrated using simulated data for composite materials with different anisotropy and damping degrees. A study of the effect of the rheologic model choice on the elastic property identification emphasizes the relevance of using a phenomenological description considering viscosity. Experimental characterizations show then the good reliability of the proposed approach. Difficulties arise experimentally for particular anisotropic media.
Speckle coherence and implications for adaptive imaging
Authors: Walker William F. , Trahey Gregg E.
Published: July 2002

Tissue speed of sound inhomogeneities cause significant degradation of medical ultrasound images. In certain cases these inhomogeneities can be modeled as a thin, spatially varying time delay screen located at the face of the transducer. Correction of such aberrators requires the addition of compensating time delays to the normal system focusing delays. These compensating delays are estimated from the arrival time differences between echoes received on different array elements. The accuracy with which these arrival time differences can be estimated is limited by the level of correlation between received speckle signals. This paper derives analytical expressions predicting the correlation between speckle signals acquired by a pulse echo system with either point or larger receive elements in the presence of near-field phase aberrations. Simulations are presented which are in good agreement with theoretical predictions. Similarities between the derived expressions and the Van Cittert–Zernike Theorem are discussed. These results indicate that near-field phase aberration correction may be far more difficult than previous analyses suggest because of the low correlation between echoes received by adjacent elements in elevation in 1.5-D arrays. Transmit aperture amplitude apodization and a new translating aperture technique are presented as methods for improving speckle correlation.
Determination of the second- and third-order elastic constants in Al from the natural frequencies
Authors: Chiroiu V. , Delsanto P. P. , Munteanu L. , Rugina C. , Scalerandi M.
Published: July 2002

The Hamiltonian approach to the calculation of vibrational modes of elastic cubic objects is exploited, including the effect of higher-order elastic constants. A technique is presented for solving the inverse problem, i.e., the determination of second- and third-order elastic constants for face cubic centered crystals by inversion of natural frequencies data. An unconstrained minimization algorithm, using gradient methods, is used to numerically solve the inverse problem. The method is applied to the case of Al alloys, since they are particularly suitable for applications of the acoustoelastic effect, which requires a knowledge of the third-order elastic constants. The efficiency and the accuracy of the method and the influence of measurement errors are discussed.
Modeling the relation between the intensity just-noticeable difference and loudness for pure tones and wideband noise
Authors: Allen Jont B. , Neely Stephen T.
Published: July 2002

A classical problem in auditory theory is the relation between the loudness L(I) and the intensity just-noticeable difference (JND) ΔI(I). The intensity JND is frequently expressed in terms of the Weber fraction defined by J(I)≡ΔI/I because it is anticipated that this ratio should be a constant (i.e., Weber’s law). Unfortunately, J(I) is not a constant for the most elementary case of the pure tone JND. Furthermore it remains unexplained why Weber’s law holds for wide-band stimuli. We explore this problem and related issues. The loudness and the intensity JND are defined in terms of the first and second moments of a proposed random decision variable called the single-trial loudness L̃(I), namely the loudness is L(I)≡EL̃(I), while the variance of the single trial loudness is σL2≡E(L̃−L)2. The JND is given by the signal detection assumption ΔL=d′σL, where we define the loudness JND ΔL(I) as the change in loudness corresponding to ΔI(I). Inspired by Hellman and Hellman’s recent theory [J. Acoust. Soc. Am. 87, 1255–1271 (1990)], we compare the Riesz [Phys. Rev. 31, 867–875 (1928)] ΔI(I) data to the Fletcher and Munson [J. Acoust. Soc. Am. 5, 82–108 (1933)] loudness growth data. We then make the same comparison for Miller’s [J. Acoust. Soc. Am. 19, 609–619 (1947)] wideband noise JND and loudness match data. Based on this comparison, we show empirically that ΔL(L)∝L1/p, where p=2 below ≈5 sones and is 1 above. Since ΔL(I) is proportional to σL, when p=2 the statistics of the single-trial loudness L̃ are Poisson-like, namely σL2∝L. This is consistent with the idea that the pure tone loudness code is based a neural discharge rate (not the auditory nerve). Furthermore, when p=1 (above about 5 sones), the internal loudness signal-to-noise ratio is constant. It is concluded that Ekman’s law (ΔL/L is constant) is true, rather than Weber’s law, in this loudness range. One of the main contributions of this paper is its attempt to integrate Fletcher’s neural excitation pattern model of loudness and signal detection theory.
Chaos in segments from Korean traditional singing and Western singing
Authors: Lee Myeong-Hwa , Lee Jeong-No , Soh Kwang-Sup
Published: July 2002

The time series of the segments from a Korean traditional song “Gwansanyungma” and a western song “La Mamma Morta” were investigated using chaotic analysis techniques. It is found that the phase portrait in the reconstructed state space of the time series of the segment from the Korean traditional song has a more complex structure in comparison with the segment from the western songs. The segment from the Korean traditional song has the correlation dimension 4.4 and two positive Lyapunov exponents which show that the dynamic related to the Korean traditional song is a high-dimensional hyperchaotic process. On the other hand, the segment from the western song with only one positive Lyapunov exponent and the correlation dimension 2.5 exhibits low-dimensional chaotic behavior.
Acoustic field interaction with a boiling system under terrestrial gravity and microgravity
Authors: Sitter J. S. , Snyder T. J. , Chung J. N. , Marston P. L.
Published: July 2002

Pool boiling experiments from a platinum wire heater in FC-72 liquid were conducted under terrestrial and microgravity conditions, both with and without the presence of a high-intensity acoustic standing wave within the fluid. The purpose of this research was to study the interaction between an acoustic field and a pool boiling system in normal gravity and microgravity. The absence of buoyancy in microgravity complicates the process of boiling. The acoustic force on a vapor bubble generated from a heated wire in a standing wave was shown to be able to play the role of buoyancy in microgravity. The microgravity environment was achieved with 0.6 and 2.1-s drop towers. The sound was transmitted through the fluid medium by means of a half wavelength sonic transducer driven at 10.18 kHz. At high enough acoustic pressure amplitudes cavitation and streaming began playing an important role in vapor bubble dynamics and heat transfer. Several different fixed heat fluxes were chosen for the microgravity experiment and the effects of acoustics on the surface temperature of the heater were recorded and the vapor bubble movement was filmed. Video images of the pool boiling processes and heat transfer data are presented.
Simple conformal methods for finite-difference time-domain modeling of pressure-release surfaces
Authors: Schneider John B. , Wagner Christopher L. , Kruhlak Robert J.
Published: July 2002

The finite-difference time-domain (FDTD) method provides a simple and accurate means of simulating a wide range of acoustic wave propagation problems. Unfortunately, the method has a voracious appetite for computational resources. For example, to accurately model scattering from a continuously varying pressure-release boundary, an FDTD grid is typically required that has a much finer discretization than is necessary to model propagation in a homogeneous space. Such a fine discretization can become prohibitive when considering large-scale problems. Two simple conformal techniques are presented for acoustic FDTD simulations of problems involving pressure-release boundaries. These techniques, which rely upon splitting velocity cells adjacent to the pressure-release boundary, significantly improve the accuracy of the results over those of the standard “staircase” representation of the boundary. These methods permit the use of a coarser FDTD grid than would otherwise be practical and yet add negligible computational cost. The improved accuracy of these split-cell techniques is shown for both a spherical scatterer and a spherical resonator.
Point vowels in Japanese mothers’ speech to infants and adults
Authors: Andruski Jean E. , Kuhl Patricia K. , Hayashi Akiko
Published: July 2002

American, Russian, and Swedish mothers produce acoustically more extreme point vowels (/i/, /u/, and /a/) when speaking to their infants than when speaking to another adult [Kuhl et al., Science 277, 684–686]. This study examines the three point vowels in Japanese mothers’ speech, and compares the acoustic structure of infant-directed (ID) and adult-directed (AD) tokens. Three target words containing /i/, /u/, and /a/ (bi:zu, batto, bu:tsu = beads, bat, boots) were recorded while mothers conversed with another native-speaking adult, and with their infants, aged either 51/2 or 81/2 months. F1, F2, and F0 were measured at vowel onset, center, and offset. Acoustic, results will be compared for AD and ID speech, and expansion of the vowel space in Japanese mothers’ speech will be examined. [Work supported by NIH HD35465-01S1.]
Three-dimensional vibration analysis of a cantilevered parallelepiped: Exact and approximate solutions
Authors: Lim C. W.
Published: July 2002

The paper investigates the hypothetical assumption of neglecting transverse normal stress in vibration analysis for cantilevered thick plates and rectangular parallelepiped. The analysis solves the three-dimensional elasticity energy functional including, as well as excluding, transverse normal stress and obtains free vibration solutions for a cantilevered parallelepiped. Although it is widely accepted, the omission of transverse normal stress is well justified in Kirchhoff–Love thin-plate theory and higher-order thick-plate models; the transverse normal stress effects and thickness extent to which the thick-plate models apply as the thickness increases are practically unknown. The inconsistency of assuming constant transverse normal displacement through thickness for thick-plate models is also addressed. The paper concludes that for a rectangular parallelepiped with thickness exceeding a certain limit, there is considerable discrepancy if transverse normal stress is neglected.
Psychoacoustic comparison of two methods for the evaluation of prominent discrete tones
Authors: Balant Anne C. , Barringer Kristin , Nobile Matthew
Published: July 2002

Two objective methods have been developed to evaluate the potential annoyance of prominent discrete tones in the noise emissions of products: (1) the tone-to-noise ratio (TNR) method [ECMA-74-1997, ANSI S1.13-1995] and (2) the prominence ratio (PR) method [ANSI S1.13]. A task group of the Inter-Committee Working Group on noise from information technology and telecommunications equipment (ITTE) is studying both procedures, with the goal of optimizing a single method. In some cases the procedures give conflicting results, especially when there are harmonics and/or multiple tones within a single critical band. ECMA-74-1997 employs a modification of the TNR method for cases in which there are two tones within the critical band. This talk will present the results of two pilot studies comparing naive listeners’ subjective ratings of signals containing discrete tones to the measured TNR and PR values. In the first pilot study, stimuli were a series of recorded machine noises. In the second study, stimuli were constructed by mixing the noise produced by axial fans with a pure tone close to the fundamental frequency of the fans. The level and frequency of the tone was varied. The results of these pilot studies and recommendations for future work will be discussed.
Mapping acoustic sensitivity about the dolphin’s head: A look at the peripheral hearing system
Authors: Brill Randall L. , Moore Patrick W. B. , Helweg David A. , Dankiewicz Lois A.
Published: July 2002

The hypothesis that echolocating dolphins best receive acoustic signals over the pan bones of the lower jaw is widely accepted. Studies in echolocation and hearing have assumed that those areas serve as the dolphin’s peripheral hearing system. The research that established that model, however, does not exclude other potential sound reception sites and suggests that additional areas of the head may be acoustically sensitive and perhaps frequency dependent. Using jawphones, relative hearing thresholds for representative frequencies (10, 30, 60, and 90 kHz) were behaviorally measured at over 40 sites on a dolphin’s head. Iso-sensitivity curves were constructed and projected onto the image of a dolphin’s head based on these measurements. The results suggest sensitivity to high frequency along the lower jaw with greater sensitivity forward of the pan bone area, sensitivity to low frequency around the external auditory meatus, and an acoustic asymmetry with greater sensitivity favoring the right side of the head. These results may correlate to underlying anatomical features and suggest a more complex peripheral hearing system than has been previously assumed.
Rheological Behavior of Dilatant (Shear-Thickening) Fluids. Part II. Mechanism and Theory
Authors: Green Richard G. , Griskey Richard G.
Published: July 2002

A theory for the rheological behavior of dilatant (shear-thickening) fluids was developed. The theory based on physical-chemical principles was shown to overcome the shortcomings of existing theories. In addition, it was found that the theory predicted the rheological behavior of dilatant (shear-thickening) fluids as affected by particle size, suspending medium characteristics, temperature, and concentration.
Rheological Implications of the Exit Pressure and Die Swell in Steady Capillary Flow of Polymer Melts. I. The Primary Normal Stress Difference and the Effect of L/D Ratio on Elastic Properties
Authors: Han C. D. , Charles M. , Philippoff W.
Published: July 2002

Apparatus which permits accurate measurement of shear stress and “exit pressure” has been constructed by the authors. Data has been obtained for high density polyethylene and polypropylene and the primary normal stress difference has been calculated by revising an equation advanced by Metzner et al. Measurements were obtained using capillaries of various L/D ratios inasmuch as there is evidence to indicate that elastic properties require a considerable flow distance to fully develop. Furthermore, the “exit pressure” has been correlated with the melt die swell which is known to depend on the L/D ratio. In addition to to the experiments with polymer melts, studies were also performed with a Newtonian fluid (Indopol H-1900) which, at room temperature, has a viscosity comparable to that of a polymer melt. These experiments demonstrated that the technique gives a zero (gauge) “exit pressure” for a Newtonian fluid. Finally, a special die was used to test Lodge's “Hole Pressure” hypothesis inasmuch as the existence of this effect would considerably influence the results. Experiments were performed using polyethylene, polypropylene, and Indopol H-1900. In no case was the “Hole Pressure” effect observed.
Stress-Strain Relations of Thermorheologically Simple Materials under Finite Deformation
Authors: Ting Edward C.
Published: July 2002

This paper studies the stress-strain relations of isotropic viscoelastic solids with temperature-dependent properties under finite deformation. The underlying derivation is an analogy to the well-known temperature-time equivalence hypothesis established for linear viscoelastic solids. Following a general discussion, stress-strain relations for small finite deformations are discussed.
Birefringence studies in die flows of an HDPE melt
Authors: Park H. J. , Kiriakidis D. G. , Mitsoulis E. , Lee K.-J.
Published: July 2002

Flow studies of a high-density polyethylene (HDPE) melt have been undertaken through planar slit dies with the purpose of establishing the birefringence pattern. Experimental results are compared with numerical solutions obtained by using an integral constitutive equation of the K-BKZ type with a spectrum of relaxation times. The material parameters have been obtained by fitting viscosity and normal stress data as measured in shear, and elongational viscosity data available in the literature. The numerical simulations have been undertaken for a long (L/2H=2) and a short (L/2H=0.5) die at 180 °C. They show that as the flow rate increases, viscoelastic effects become important and manifest themselves in delayed relaxation of stresses along the slit and in stress overshoots at the die exit. This behavior is in close agreement with experimental birefringence patterns and in sharp contrast with purely viscous simulations which cannot predict such strong viscoelastic phenomena. Elastic recovery is also captured in an enhanced extrudate swell which is always higher for the short die.
Continuum dynamic behavior of homogeneous liquid-crystalline polymers under the imposition of shear and magnetic fields
Authors: Andrews N. C. , Edwards B. J. , McHugh A. J.
Published: July 2002

An analysis of the dynamic behavior of polymeric liquid crystals is given in terms of a second-rank order parameter tensor describing the orientational state of the local microstructure. The continuum equations governing the dynamics of the material are analyzed under both steady-state and transient conditions for isotropic and liquid-crystalline fluids subjected to shear and magnetic fields. Analysis reveals that a great variety of dynamic behavior for liquid-crystalline materials can be accommodated within the framework of a continuum theory in terms of a second-rank order parameter tensor, and that this dynamic behavior approximates well the orientational behavior obtained with the more complex distribution function theories. Under some conditions the associated rheological behavior of the continuum theory exhibits discrepancies in the normal stress behavior compared to rheological calculations based on the distribution function theory. For simultaneous application of shear and magnetic fields, both the direction and the strength of the magnetic field play a major role in determining the dynamic system response.
Nostochopsis
Authors: Golubic Stjepko , Hoffmann Lucien
Published: May 2022

Nos.toch.op'sis. N.L. neut. n.Nostoc, a cyanobacterial genus; suff.‐opsis, similar to; from Gr. fem. n.opsis, aspect, appearance; N.L. fem. n.Nostochopsis, similar toNostoc.

Cyanobacteria / Subsection V / Nostochopsidaceae / Nostochopsis

Nostochopsisis a filamentous cyanobacterium with true branching (Subsection. V. in Rippka et al., 1979). The colonies are gelatinous, firm, and internally hollow. Trichomes are uniseriate with lateral T‐branches of two types: with unlimited and limited growth (1–3 cells), the latter with a terminal single‐pore heterocyst. Branch limited to a single cell that differentiates into a lateral heterocyst; intercalary heterocysts are less common.

Type species:Nostochopsis lobatusWood ex Bornet and Flahault 1886, as originally described, was accepted and slightly modified by Geitler (1932, p. 475). The species name was corrected for gender by Komárek (2013, p. 546), so that in some sources it is entered asN. lobata. Nostochopsis lobatuswas collected in freshwater environments of Spain (Moreno et al., 2012), India, (Tiwari, 1978), Thailand (Thiamdao et al., 2012), and Argentina (Cáceres, 1973; Diaga et al., 2014). It was studied both using field‐collected and cultured materials; the growth was found to be modified depending on the culture conditions (Yamaguchi and Koketsu, 2016). The organism produced intercalary and more commonly terminal and lateral heterocysts.
Crocosphaera
Authors: Zehr Jonathan P. , Foster Rachel A. , Waterbury John , Webb Eric A.
Published: May 2022

Cro.co.sphae'ra. Gr. xxxxx n
krokos
, the crocus, orange‐colored; Gr. fem. n.
sphaera
, a ball or sphere; N.L. fem. n.
Crococsphaera
, an orange ball or sphere, M.L. fem. n.,
Crocosphaera
, an orange ball due to autofluorescence of high urobilin phycoerythrin.

Cyanobacteria / Subsection I / Incertae Sedis / Crocosphaera

Coccoid, pigmented nonmotile cyanobacterial cells found in open ocean plankton that range in diameter from 2 to 6 μm, although larger cells have been reported in the environment. Cells occur singly or in small clusters and reproduce in one plane. Several known strains vary primarily in size, are capable of extracellular polysaccharide (EPS) synthesis, and comprise two phenotypic groups. Aerobic oxygenic phototrophs that fix carbon dioxide using the ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBisCO) pathway. Can grow with atmospheric nitrogen (N
2
) as the sole nitrogen source with an oxygen‐sensitive nitrogenase. Fix N
2
primarily in the dark period of a light–dark cycle under atmospheric concentrations of oxygen. Evolve molecular hydrogen (H
2
) and contain an uptake hydrogenase. In addition to chlorophylls
a
and
b
possess phycoerythrin with high phycourobilin content. Gas vacuoles are absent. Capable of secondary metabolite (possible toxin) production since they possess polyketide synthesis (PKS) and nonribosomal polyketide synthesis (NRPS) genes. Synthesize trehalose. Are ecologically important as N
2
‐fixers but are limited to the tropical oceans or seasonally in the subtropics due to restricted temperature range permitting growth.

DNA G + C content (mol%)
: 30.6–31.0 (
T
m
) (WH8501 and WH8502); 37.1–37.7 (genome sequences).

Type species
:
Crocosphaera watsonii
Mareš et al. 2019.
Cognitive profile in idiopathic autonomic failure: relation with white matter hyperintensities and neurofilament levels
Authors: Cani Ilaria , Sambati Luisa , Bartiromo Fiorina , Asioli Gian Maria , Baiardi Simone , Belotti Laura M. B. , Giannini Giulia , Guaraldi Pietro , Quadalti Corinne , Romano Luciano , Lodi Raffaele , Parchi Piero , Cortelli Pietro , Tonon Caterina , Calandra‐Buonaura Giovanna
Published: May 2022

Objective

To disclose the nature of cognitive deficits in a cohort of patients with idiopathic autonomic failure (IAF) by exploring the relation among cognitive functions, cardiovascular autonomic failure (AF) and clinical progression to another α‐synucleinopathy (phenoconversion).

Methods

We retrospectively identified all patients with a clinical diagnosis of IAF who underwent a comprehensive neuropsychological evaluation, clinical examination and cardiovascular autonomic tests from the IAF‐BO cohort. Brain magnetic resonance imaging (MRI) studies and cerebrospinal fluid (CSF) analysis, including neurofilament light chain (NfL), Alzheimer disease core biomarkers, and α‐synuclein seeding activity were further evaluated when available.

Correlations among cognitive functions, clinical features, cardiovascular AF, cerebral white matter hyperintensities (WMH) load, and CSF biomarkers were estimated using Spearman correlation coefficient.

Results

Thirteen out of 30 (43%) patients with IAF displayed cognitive deficits (CI) mainly concerning executive functioning. Seven out of 30 (23%) met the criteria for mild cognitive impairment (MCI).

The diagnosis of CI and MCI was not associated with phenoconversion or autonomic function parameters, including duration and severity of neurogenic orthostatic hypotension, presence and severity of supine hypertension, and nocturnal dipper profile.

Twenty patients underwent a brain MRI and CSF analysis. MCI was related to WMH load (r = 0.549) and NfL levels (r = 0.656), while autonomic function parameters were not associated with either WMH or NfL levels.

Interpretation

Cardiovascular AF and phenoconversion, underlying the spreading of neurodegeneration to the central nervous system, were not independent drivers of cognitive dysfunction in IAF. We identified WMH load and NfL levels as potential biomarkers of the neural network disruption associated with cognitive impairment in patients with IAF.
Response of plasmamicroRNAsto nusinersen treatment in patients withSMA
Authors: Zaharieva Irina T. , Scoto Mariacristina , Aragon‐Gawinska Karolina , Ridout Deborah , Doreste Bruno , Servais Laurent , Muntoni Francesco , Zhou Haiyan
Published: May 2022

Objective

Spinal muscular atrophy (SMA) is a common genetic cause of infant mortality. Nusinersen treatment ameliorates the clinical outcome of SMA, however, some patients respond well, while others have limited response. We investigated microRNAs in blood samples from SMA patients and their response to nusinersen treatment evaluating the potential of circulating microRNAs as biomarkers for SMA.

Methods

In a discovery cohort study, microRNA next‐generation sequencing was performed in blood samples from SMA patients (SMA type 2,n = 10; SMA type 3,n = 10) and controls (n = 7). The dysregulated microRNAs were further analysed in the therapeutic response cohort comprised of SMA type 1 patients (n = 22) who had received nusinersen treatment, at three time points along the treatment course (baseline, 2 and 6 months of treatment). The levels of the studied microRNAs were correlated to the SMA clinical outcome measures.

Results

In the discovery cohort, 69 microRNAs were dysregulated between SMA patients and controls. In the therapeutic response cohort, the baseline plasma levels of miR‐107, miR‐142‐5p, miR‐335‐5p, miR‐423‐3p, miR‐660‐5p, miR‐378a‐3p and miR‐23a‐3p were associated with the 2 and 6 months response to nusinersen treatment. Furthermore, the levels of miR‐107, miR‐142‐5p, miR‐335‐5p, miR‐423‐3p, miR‐660‐5p and miR‐378‐3p at 2 months of treatment were associated with the response after 6 months of nusinersen treatment.

Interpretation

Blood microRNAs could be used as biomarkers to indicate SMA patients’ response to nusinersen and to monitor the efficacy of the therapeutic intervention. In addition, some of these microRNAs provide insight into processes involved in SMA that could be exploited as novel therapeutic targets.
Atomic Heterointerface Engineering of Ni2P‐NiSe2 Nanosheets Coupled ZnP‐Based Arrays for High‐Efficiency Solar‐Assisted Water Splitting
Authors: Chang Kai , Tran Duy Thanh , Wang Jingqiang , Prabhakaran Sampath , Kim Do Hwan , Kim Nam Hoon , Lee Joong Hee
Published: May 2022

In this study, heterogeneous nickel phosphide‐nickel selenide (Ni2P‐NiSe2) nanosheets are constructed to coat zinc phosphide‐based nanorods (ZnP NRs) under a unique core@shell architecture, which acts as a highly active multifunctional catalyst toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The catalyst exhibits an overpotential of 79 mV at 10 mA cm–2 for HER and 326 mV at 100 mA cm–2 for OER in freshwater under an alkaline condition. The formation of an open 3D channel architecture derived from highly conductive ZnP@Ni2P‐NiSe2 nanorods attached nickel foam generates more exposed active sites and promotes fast mass transport. In addition, density functional theory study reveals a synergistic effect between Ni2P and NiSe2 phase to reduce adsorption free energy and increase the electronic conductivity, thereby accelerating the catalytic reaction kinetics. An electrolyzer of the ZnP@Ni2P‐NiSe2(+,‐) requires only cell voltages of 1.54 V (1.43 V) and 1.51 V (1.44 V) to deliver 10 mA cm–2 in freshwater and mimic seawater at 25 °C (75 °C), respectively, along with prospective long‐term stability. Furthermore, the solar energy‐assisted water splitting process demonstrates a solar‐to‐hydrogen efficiency of 19.75%, implying that the catalyst is an effective and low‐cost candidate for water splitting.
Resolving the Role of Configurational Entropy in Improving Cycling Performance of Multicomponent Hexacyanoferrate Cathodes for Sodium‐Ion Batteries
Authors: Ma Yanjiao , Hu Yang , Pramudya Yohanes , Diemant Thomas , Wang Qingsong , Goonetilleke Damian , Tang Yushu , Zhou Bei , Hahn Horst , Wenzel Wolfgang , Fichtner Maximilian , Ma Yuan , Breitung Ben , Brezesinski Torsten
Published: May 2022

Mn‐based hexacyanoferrate (Mn‐HCF) cathodes for Na‐ion batteries usually suffer from poor reversibility and capacity decay resulting from unfavorable phase transitions and structural degradation during cycling. To address this issue, the high‐entropy concept is here applied to Mn‐HCF materials, significantly improving the sodium storage capabilities of this system via a solid‐solution mechanism with minor crystallographic changes upon de‐/sodiation. Complementary structural, electrochemical, and computational characterization methods are used to compare the behavior of high‐, medium‐, and low‐entropy multicomponent Mn‐HCFs resolving, to our knowledge for the first time, the link between configurational entropy/compositional disorder (entropy‐mediated suppression of phase transitions, etc.) and cycling performance/stability in this promising class of next‐generation cathode materials.
Data‐Driven High‐Throughput Rational Design of Double‐Atom Catalysts for Oxygen Evolution and Reduction
Authors: Wu Lianping , Guo Tian , Li Teng
Published: May 2022

Surging interests exist in double‐atom catalysts (DACs), which not only inherit the advantages of single‐atom catalysts (SACs) (e.g., ultimate atomic utilization, high activity, and selectivity) but also overcome the drawbacks of SACs (e.g., low loading and isolated active site). The design of DACs, however, remains cost‐prohibitive for both experimental and computational studies, due to their huge design space. Herein, by means of density functional theory (DFT) and topological information‐based machine‐learning (ML) algorithms, we present a data‐driven high‐throughput design principle to evaluate the stability and activity of 16 767 DACs for oxygen evolution (OER) and oxygen reduction (ORR) reactions. The rational design reveals 511 types of DACs with OER activity superior to IrO2(110), 855 types of DACs with ORR activity superior to Pt (111), and 248 bifunctional DACs with high catalytic performance for both OER and ORR. An intrinsic descriptor is revealed to correlate the catalytic activity of a DAC with the electronic structures of the DAC and its bonding carbon surface structure. This data‐driven high‐throughput approach not only yields remarkable prediction precision (>0.926 R‐squared) but also enables a notable 144 000‐fold reduction of screening time compared with pure DFT calculations, holding promise to drastically accelerate the design of high‐performance DACs.