bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of convergence and extension by cell intercalation
Authors: Keller Ray , Davidson Lance , Edlund Anna , Elul Tamira , Ezin Max , Shook David , Skoglund Paul
Published: July 2002

The cells of many embryonic tissues actively narrow in one dimension (convergence) and lengthen in the perpendicular dimension (extension). Convergence and extension are ubiquitous and important tissue movements in metazoan morphogenesis. In vertebrates, the dorsal axial and paraxial mesodermal tissues, the notochordal and somitic mesoderm, converge and extend. In amphibians as well as a number of other organisms where these movements appear, they occur by mediolateral cell intercalation, the rearrangement of cells along the mediolateral axis to produce an array that is narrower in this axis and longer in the anteroposterior axis. In amphibians, mesodermal cell intercalation is driven by bipolar, mediolaterally directed protrusive activity, which appears to exert traction on adjacent cells and pulls the cells between one another. In addition, the notochordal–somitic boundary functions in convergence and extension by ‘capturing’ notochordal cells as they contact the boundary, thus elongating the boundary. The prospective neural tissue also actively converges and extends parallel with the mesoderm. In contrast to the mesoderm, cell intercalation in the neural plate normally occurs by monopolar protrusive activity directed medially, towards the midline notoplate–floor–plate region. In contrast, the notoplate–floor–plate region appears to converge and extend by adhering to and being towed by or perhaps migrating on the underlying notochord. Converging and extending mesoderm stiffens by a factor of three or four and exerts up to 0.6 μN force. Therefore, active, force–producing convergent extension, the mechanism of cell intercalation, requires a mechanism to actively pull cells between one another while maintaining a tissue stiffness sufficient to push with a substantial force. Based on the evidence thus far, a cell–cell traction model of intercalation is described. The essential elements of such a morphogenic machine appear to be (i) bipolar, mediolaterally orientated or monopolar, medially directed protrusive activity; (ii) this protrusive activity results in mediolaterally orientated or medially directed traction of cells on one another; (iii) tractive protrusions are confined to the ends of the cells; (iv) a mechanically stable cell cortex over the bulk of the cell body which serves as a movable substratum for the orientated or directed cell traction. The implications of this model for cell adhesion, regulation of cell motility and cell polarity, and cell and tissue biomechanics are discussed.
Large–scale heterogeneity of the fossil record: implications for Phanerozoic biodiversity studies
Authors: Smith Andrew B.
Published: July 2002

Patterns of origination, extinction and standing diversity through time have been inferred from tallies of taxa preserved in the fossil record. This approach assumes that sampling of the fossil record is effectively uniform over time. Although recent evidence suggests that our sampling of the available rock record has indeed been very thorough and effective, there is also overwhelming evidence that the rock record available for sampling is itself distorted by major systematic biases.

Data on rock outcrop area compiled for post–Palaeozoic sediments from Western Europe at stage level are presented. These show a strongly cyclical pattern corresponding to first– and second–order sequence stratigraphical depositional cycles. Standing diversity increases over time and, at the coarsest scale, is decoupled from surface outcrop area. This increasing trend can therefore be considered a real pattern. Changes in standing diversity and origination rates over time–scales measured in tens of millions of years, however, are strongly correlated with surface outcrop area. Extinction peaks conform to a random–walk model, but larger peaks occur at just two positions with respect to second–order stratigraphical sequences, towards the culmination of stacked transgressive system tracts and close to system bases, precisely the positions where taxonomic last occurrences are predicted to cluster under a random distribution model.

Many of the taxonomic patterns that have been described from the fossil record conform to a species–area effect. Whether this arises primarily from sampling bias, or from changing surface area of marine shelf seas through time and its effect on biodiversity, remains problematic.
Tolerance and chronic rejection
Authors: Womer Karl L. , Lee Richard S. , Madsen Joren C. , Sayegh Mohamed H.
Published: July 2002

The most common cause of chronic allograft loss is an incompletely understood clinicopathological entity called chronic rejection (CR). Recent reports suggest an improvement in long–term renal allograft survival, although it is not clear from these data whether a true reduction of biopsy–proven CR has occurred. Although newer immunosuppressive medications have greatly reduced the incidence of acute rejection (AR) in the early post–transplantation period, the ideal therapy for both AR and CR would be to achieve a state of tolerance. By definition, such a state should allow for indefinite allograft survival, with no histopathological evidence of CR, despite immunocompetence in the host (i.e. without the need for chronic immunosuppression). Although several experimental studies are able to achieve tolerance, with clear improvement in allograft survival, detailed studies on graft function and morphology are often not included. This review will discuss possible ways that tolerance induction could lead to a CR–free state. General mechanisms of CR and transplantation tolerance induction are discussed as well as the difficulties in translating small animals studies into large animals and humans.
Monitoring and surveillance for rare health-related events: a review from the veterinary perspective
Authors: Doherr M.G. , Audige L.
Published: July 2002

Disease monitoring and surveillance systems (MOSSs) have become one of the major components of veterinary activity. Such systems are used to assess the existing levels of prevalence, the effectiveness of control programmes and, after disease eradication, to document the continued absence of disease from a given region or zone. With decreasing disease or infection prevalence, traditional approaches become less reliable and increasingly costly. The objective of this work was to summarize and discuss methodological issues related to veterinary (animal health) MOSSs. There are considerable inconsistencies in the use of the terms ‘monitoring’ and ‘surveillance’. Passive as well as active MOSS have their disadvantages when used for rare health–related events such as emerging and re–emerging diseases. There is a need for evaluation and improvement of these approaches. Integrated systems that call for the use of several parallel surveillance activities seem to be the favoured approach, and analytical methods to combine MOSS data from various sources into a population prevalence, or probability of disease freedom, are under development. The health and safety of the animal and human generations depends on our continuous ability to detect, monitor and control newly emerging or re–emerging livestock diseases and zoonoses rapidly. Uniform surveillance definitions, sound scientifically based approaches that use the resources and data available, and a pool of researchers and veterinary public health officials with sufficient training in epidemiology, are critically important to handle this challenging task.
Embryology of the lamprey and evolution of the vertebrate jaw: insights from molecular and developmental perspectives
Authors: Kuratani Shigeru , Nobusada Yoshiaki , Horigome Naoto , Shigetani Yasuyo
Published: July 2002

Evolution of the vertebrate jaw has been reviewed and discussed based on the developmental pattern of the Japanese marine lamprey,Lampetra japonica. Though it never forms a jointed jaw apparatus, theL. japonicaembryo exhibits the typical embryonic structure as well as the conserved regulatory gene expression patterns of vertebrates. The lamprey therefore shares the phylotype of vertebrates, the conserved embryonic pattern that appears at pharyngula stage, rather than representing an intermediate evolutionary state. Both gnathostomes and lampreys exhibit a tripartite configuration of the rostral–most crest–derived ectomesenchyme, each part occupying an anatomically equivalent site. Differentiated oral structure becomes apparent in post–pharyngula development. Due to the solid nasohypophyseal plate, the post–optic ectomesenchyme of the lamprey fails to grow rostromedially to form the medial nasal septum as in gnathostomes, but forms the upper lip instead. The gnathostome jaw may thus have arisen through a process of ontogenetic repatterning, in which a heterotopic shift of mesenchyme–epithelial relationships would have been involved. Further identification of shifts in tissue interaction and expression of regulatory genes are necessary to describe the evolution of the jaw fully from the standpoint of evolutionary developmental biology.
Optimization of x‐ray imaging geometry (with specific application to flat‐panel cone‐beam computed tomography)
Authors: Siewerdsen Jeffrey H. , Jaffray David A.
Published: July 2002

A theoretical method is presented that allows identification of optimal x‐ray imaging geometry, considering the effects of x‐ray source distribution, imaging task, x‐ray scatter, and imager detective quantum efficiency (DQE). Each of these factors is incorporated into the ICRU‐recommended figure of merit for image quality, the detectability index, which is maximized to determine the optimal system configuration. Cascaded systems analysis of flat‐panel imagers (FPIs) is extended to incorporate the effects of x‐ray scatter directly in the DQE, showing that x‐ray scatter degrades DQE as an additive noise source. Optimal magnification is computed for FPI configurations appropriate to (but not limited to) cone‐beam computed tomography (CBCT). The sensitivity of the results is examined as a function of focal spot size, imaging task (e.g., ideal observer detection or discrimination tasks), x‐ray scatter fraction, detector resolution, and additive noise. Nominal conditions for FPI‐CBCT result in optimal magnification of ∼1.4–1.6, depending primarily on the magnitude of the x‐ray scatter fraction. The methodology is sufficiently general that examination of optimal geometry for other FPI applications (e.g., chest radiography, fluoroscopy, and mammography) is possible. The degree to which increased exposure can be used to compensate for x‐ray scatter degradation is quantified.
Characteristics of bremsstrahlung in electron beams
Authors: Zhu Timothy C. , Das Indra J. , Bjärngard Bengt E.
Published: July 2002

Clinical electron beams contain an admixture of bremsstrahlung produced in structures in the accelerator head, in field‐defining cerrobend or lead cutouts, and in the irradiated patient or water phantom. Accurate knowledge of these components is important for dose calculations and treatment planning. In this study, the bremsstrahlung components are separated for electron beams (energy 6–22 MeV, diameter 0–5 cm) using measurements in water and calculations. The results show that bremsstrahlung from the accelerator head dominates and increases with field size for electron beams generated by accelerators equipped with scattering foils. The bremsstrahlung from the field‐defining cerrobend accounts for 10% to 30% of the total bremsstrahlung and decreases with increasing beam radius. The bremsstrahlung is softer than the x‐ray beams of corresponding nominal energy since the latter are hardened by the flattening filter. For the 6, 12, and 22 MeV electron beams, the effective attenuation coefficients in water for the bremsstrahlung are 0.058, 0.050, and 0.043The depths of maximum dose at 100 cm SSD are 0.8, 1.7, and 3.0 cm. The position of the virtual source of the bremsstrahlung shifts downstream from the nominal source position by 20, 13, 5.6 cm, respectively. The lateral bremsstrahlung dose distribution is more forward‐peaked for higher electron energy. The bremsstrahlung components could be described for any machine by a set of simple measurements and can be modeled by an analytical expression.
A method for calculating the dose to a multi‐storey building due to radiation scattered from the roof of an adjacent radiotherapy facility
Authors: Zavgorodni S. F.
Published: July 2002

With modern urbanization trends, situations occur where a general‐purpose multi‐storey building would have to be constructed adjacent to a radiotherapy facility. In cases where the building would not be in the primary x‐ray beam, “skyshine” radiation is normally accounted for. The radiation scattered from the roof side‐wise towards the building can also be a major contributing factor. However, neither the NCRP reports nor recently published literature considered this. The current paper presents a simple formula to calculate the dose contribution from scattered radiation in such circumstances. This equation includes workload, roof thickness, field size, distance to the reference point and a normalized angular photon distribution functionwhere θ is the angle between central axis of the primary beam and photon direction. The latter was calculated by the Monte Carlo method (EGS4 code) for each treatment machine in our department. For angles θ exceeding ∼20 degrees (i.e., outside the primary beam and its penumbra) the angular distribution functionwas found to have little dependence on the shielding barrier thickness and the beam energy. An analytical approximation of this function has been obtained. Measurements have been performed to verify this calculation technique. An agreement within 40% was found between calculated and measured dose rates. The latter combined the scattered radiation and the dose from “skyshine” radiation. Some overestimation of the dose resulted from uncertainties in the radiotherapy building drawings and in evaluation of the “skyshine” contribution.
The effect of scattering foil parameters on electron‐beam Monte Carlo calculations
Authors: Bieda Michael R. , Antolak John A. , Hogstrom Kenneth R.
Published: July 2002

The sensitivity of electron‐beam Monte Carlo dose calculations to scattering foil geometrical parameters is described. A method for resolving discrepancies between Monte Carlo calculation and measured data in a systematic manner is also described. As part of a project to investigate the utility of Monte Carlo methods for calculating data required for commissioning electron beams, a large discrepancy between measured and calculated 20 MeV cross‐beam profiles for the largest field size was found. It was hypothesized that the discrepancy was due to incorrect input data and that better agreement between calculation and measurement could be achieved with small changes in the scattering foil system geometry. Four parameters describing the foil system were varied individually until better agreement between calculation and measurement was achieved, and the percentage change in the parameter was tabulated as an indication of the sensitivity of the model to that parameter. The accelerator model for the 20 MeV electron beam was most sensitive to the distance between the scattering foils and to a slightly lesser extent, to the width of the shaped secondary scattering foil. Changes to the primary or secondary foil thickness also significantly modified the falloff and bremsstrahlung component of depth dose, which was unacceptable for the present case. Therefore, the distance between the two scattering foils was changed in our calculations, which the manufacturer later confirmed was indeed the case. For 6 and 12 MeV electron beams, the change was not nearly as significant. It was concluded that Monte Carlo calculations for higher‐energy beams and larger field sizes are most sensitive to the geometric configuration of the scattering foil system and should therefore be calculated first to help verify the accuracy of the geometric information.
Experimental derivation of wall correction factors for ionization chambers used in high dose rate source calibration
Authors: Maréchal M. H. , de Almeida C. E. , Ferreira I. H. , Sibata C. H.
Published: July 2002

At present there are no specific primary standards forhigh dose rate sources used in brachytherapy. Traceability to primary standards is guaranteed through the method recommended by the AAPM that derives the air kerma calibration factor for thegamma rays as the average of the air kerma calibration factors for x‐rays andgamma‐rays or the Maréchal et al. method that uses the energy‐weighted air kerma calibration factors for 250 kV x rays andgamma rays as the air kerma calibration factor for thegamma rays. In order to use these methods, it is necessary to use the same buildup cap for all energies and the appropriate wall correction factor for each chamber. This work describes experimental work used to derive thefor four different ionization chambers and different buildup cap materials for the three energies involved in the Maréchal et al. method. Thefor the two most common ionization chambers used in hospitals, the Farmer NE 2571 and PTW N30001 is 0.995 and 0.997, respectively, for 250 kV x rays, 0.982 and 0.985 forgamma rays, and 0.979 and 0.991 forgamma rays, all for a PMMA build‐up cap of 0.550 gm cm−2. A comparison between the experimental values and Monte Carlo calculations shows an agreement better than 0.9%. Availability of thecorrection factors for all commercial chambers allows users of the in‐air calibration jig, provided by the manufacturer, to alternatively use the Maréchal et al. method. Calibration laboratories may also used this method for calibration of a well‐type ionization chamber with a comparable accuracy to the AAPM method.
Optimizing the shape of ultrasound transducers for interstitial thermal ablation
Authors: Lafon Cyril , Melo de Lima David , Theillère Yves , Prat Frédéric , Chapelon Jean‐Yves , Cathignol Dominique
Published: July 2002

Heat deposition by interstitial routes, especially with ultrasound‐based instruments, is becoming a valuable therapeutic option for the treatments of sites, which are difficult to access from outside of the body. The active part of most interstitial ultrasound applicators described in the literature is logically tubular to induce cylindrical volumes of coagulation necrosis. Because the pressure generated by such tubular transducers falls off rapidly with radial distance, we previously proposed using a rotating plane transducer. For a plane wave, the pressure fall‐off is only due to attenuation, which makes deeper lesions and shorter treatment times possible. This work represents an advance in the development of ultrasound applicators designed for interstitial applications. This new applicator used a rotating slightly focused transducer. A brief theoretical analysis resulted in the choice of a long focal distance of 22 mm to obtain a nearly constant pressure all along the therapeutic depth. To experimentally validate this focal distance, pressure measurements were made in a tissue mimicking liquid phantom and the results were compared with those obtained with a plane transducer.In vitroexperiments showed that necrosis could be induced at a depth of 15 mm. In the same conditions, the greatest depth attained with a plane transducer was only 10 mm. Because each individual lesion is narrower, more lesions and more time are required to necrose a cylindrical volume. The main advantage of this new type of applicator is that it can be used to induce necrosis at a greater depth without varying either the frequency, the intensity or the transducer cooling efficiency.
Calculation of photon energy and dose distributions in a 50 MV scanned photon beam for different target configurations and scan patterns
Authors: Sätherberg Anders , Karlsson Mikael
Published: July 2002

A method to characterize the energy distribution in the whole photon field is valuable when designing an accelerator for choosing target and flattening filter or scan pattern. Another field of application is beam characterization for treatment planning systems or other dosimetric purposes. This work is focused on the energy distribution in different 50 MV bremsstrahlung beams with different scanning of electrons on three different targets. Fluence differential in energy and angle at the exit of each target has been determined by Monte Carlo calculations for a narrow beam. Data for broad beams were obtained by convolution of the narrow beams with different scan patterns. Photon energy fluence differential in energy at SSD 100 were thus found to be rather different for the targets studied. The results are presented as mean energy profiles and narrow beam half‐value layer (HVL) in water. Two different experimental setups were used to measure HVL at the central axis and at off‐axis positions. The two methods gave results which differ by 5%–6% and the calculated data where within these experimental results. In conclusion, the presented method for characterization of the photon field energy distribution is well within the experimental results and can thus be used to improve accelerator design or dosimetric calculations, e.g., for treatment planning.
Preliminary study of a metal/ portal detector
Authors: Falco Tony , Wang Hui , Fallone B. G.
Published: July 2002

A feasibility study has been performed on metal/amorphous selenium detectors for megavoltage portal imaging. The metal plates of the detectors were positioned facing the incident 6 MV and Co‐60 photon spectra. The detectors consist of various thicknesses (0.15 mm, 0.30 mm, and 0.50 mm) of amorphous selenium (‐Se) deposited on metal plates of varying thicknesses: aluminum (2.0 mm), copper (1.0 mm and 1.5 mm), stainless steel (0.9 mm), or glass (1.1 mm). The detectors were charged prior to irradiation by corona methods, and the portal images were subsequently digitized after irradiation with a noncontact electrostatic probe. The sensitivity of the detectors to dose, electric field across the‐Se layer, metal plate type and‐Se thickness, was studied. The electrostatic voltage remaining on the‐Se layer was found, both theoretically and experimentally, to exhibit a cubic relationship with respect to dose. An increase in electric field increases the sensitivity (gradient of the‐Se surface voltage vs dose curve) and dynamic range of the resultant image. An increase in‐Se thickness, however, although also increasing the sensitivity, decreases the dynamic range. The metal plate types and thicknesses within the range studied do not have a significant affect on detector sensitivity. Image quality and contrast resolution of the detector were evaluated with a contrast‐detail phantom and compared to commercially available film based and electronic portal imaging devices. Image quality of the metal/‐Se detector as a function of dose was studied by discharging the‐Se to various fractions of its initial charge, and as expected, increases with dose due to a decrease in quantum noise. Contrast‐detail images obtained by metal/‐Se detectors are superior to those obtained at higher dose levels by other commercial systems.
A simple algorithm for planar image registration in radiation therapy
Authors: Cai Jialing , Chu James C. H. , Saxena V. Amod. , Lanzl Lawrence H.
Published: July 2002

A simple algorithm is presented for planar image registration and the method is applied to the simulator and portal image registration for patient setup verification in radiation therapy. Basically, the algorithm follows the concept proposed by Balter et al. [Med. Phys.19, 329–334 (1992)], which converts the problem of open curve registration into matching a series of points along the curves. Balter's algorithm consists of three steps: (1) to determine a common starting point for each curve pair, (2) acquire two corresponding point sets along each curve, and (3) obtain a global transform matrix by matching two point sets. We integrate all three steps into one simple procedure which fits the sampled points along the intended curve pair by taking the relative path length shift as an independent fitting parameter. After being modified, the algorithm is able to take the different magnification factors of images into account, and it avoids curvature calculations. Numerical simulation as well as clinical and phantom images have been utilized to test the accuracy of the algorithm. The typical errors are less than 1 mm in translation and 1° in rotation. We also made a comparison study with the chamfer method. The results of the two methods agree to within 0.5 mm in translation and 0.5° in rotation.
Electron dose calculation using multiple‐scattering theory: A hybrid electron pencil‐beam model
Authors: Zhengming Luo , Jette David , Walker Suzan
Published: July 2002

We have embedded the bipartition model into Fermi–Eyges multiple–scattering theory to produce a more accurate hybrid electron pencil‐beam model, by using the fact that away from the edges of a large field, the electron distribution function exactly equals that for an infinitely wide electron beam. The bipartition model calculates various electron transport quantities in a homogeneous or horizontally layered medium with very high accuracy, for an infinitely broad beam. In our hybrid model, we use the bipartition model to calculate the longitudinal part of the pencil‐beam distribution function, and the Fermi–Eyges theory to calculate its transverse part. Doing this allows calculation not only of dose distribution, but also of such quantities as electron fluence distribution, energy spectrum, angular distribution, and electron‐charge distribution. Using the hybrid electron pencil‐beam model, we have calculated the dose distribution for collimated electron beams and compared them with experimental data, for rectangular fields.
Boron neutron capture synovectomy: Treatment of rheumatoid arthritis based on the nuclear reaction
Authors: Yanch J. C. , Shortkroff S. , Shefer R. E. , Johnson S. , Binello E. , Gierga D. , Jones A. G. , Young G. , Vivieros C. , Davison A. , Sledge C.
Published: July 2002

A novel application of thenuclear reaction for the treatment of rheumatoid arthritis is under investigation. Rheumatoid arthritis is characterized by a painful inflammation of the membrane (synovium) lining articular joints. Since the tissue targeted for treatment is the diseased synovial membrane and the goal is synovial ablation (“synovectomy”), the proposed treatment is called Boron Neutron Capture Synovectomy. Development of this therapeutic modality has been carried out in a number of areas, including theex vivoandin vivoevaluation ofin arthritic synovium, and the design and construction of a dedicated neutron beam assembly for joint irradiation.Ex vivoevaluation of boron uptake in human arthritic synovium usinghas demonstrated thatconcentrations of 550–2400 ppm are repeatedly obtained. Preliminaryin vivoexperiments in an arthritic rabbit model have shown that synovial boron concentrations of approximately 265–950 ppm are obtained at 15 min post intra‐articular injection. With these uptake levels experimental evaluation of the efficacy of BNCS in the treatment of rheumatoid arthritis in an animal model can be carried out. Optimal neutron beams suitable for joint irradiation are shown to be lower in energy than those used for BNCT. An assembly comprising a graphite reflector surrounding amoderator has been designed, constructed, and installed on the 4.1 MeV tandem electrostatic accelerator at MIT's Laboratory for Accelerator Beam Applications. Monte Carlo calculations predict a total therapy time of between 8.4 and 31 min for the human knee, depending on the charged particle reaction used; a particle beam current of 1 mA is assumed. Therapy times to treat a human finger joint range from 4 to 14 min for a 1 mA accelerator current. These treatment times are based on averagein vivouptake levels (observed experimentally in the rabbit knee) of 950 ppm and a 10 000 RBE‐cGy treatment dose. It is concluded that Boron Neutron Capture Synovectomy, consisting of intra‐articular injection of a‐labeled compound followed by neutron irradiation of the joint, has considerable potential as a means of treating rheumatoid arthritis.
Calculating photon beam characteristics with Monte Carlo techniques
Authors: van der Zee W. , Welleweerd J.
Published: July 2002

This study describes the results from a simulation of a 10 MV photon beam from a medical linac using theBEAMcode. To check the quality of the generated photon beam, the characteristics of this beam (depth dose curve, cross profiles, and output factors) have been calculated and compared to measured data. By splitting up the radiation head in two parts, thetarget sectionand thecollimator sectioncalculation times were long, but acceptable when aiming at phase space files containing some 5 million particles. Given the number of particles evaluated, the accuracy of all data was around 2%. Analysis of the phase space files for different field size supports results from previous studies about contaminant particles and sources for scattered radiation for photon beams from medical linacs. The total scatter output factoras well as the collimator scatter output factorhave been calculated within 2% of measurements. Also, the ratio between dose at a reference point for the full scatter situation and the no‐scatter situation has been calculated correctly. All depth dose curves and cross profiles have also been calculated correctly, although with only moderate statistics. Improvements are possible by increasing the number of particles in the simulations (up to 50 million for the largest field size) at least 4–8 times, although calculation times will increase with the same factor. Nevertheless, the method proved itself as reliable. Still, the accuracy should be improved to 1% or better. This is necessary as we plan to use Monte Carlo simulations to benchmark three‐dimensional radiotherapy planning systems. By increasing the number of particles in the phase space files and subsequently increasing the number of particles in each simulation, this 1% accuracy will be achieved. The easy way to increase the number of particles in a simulation by increasing the number of times phase space files, which were already recycled ten times, are reused from ten times (this study) to 40 times or more will not work, as it introduces artifacts, especially in the cross profiles.
A point process approach to assess the frequency dependence of ultrasound backscattering by aggregating red blood cells
Authors: Savéry David , Cloutier Guy
Published: July 2002

To study the shear-thinning rheological behavior of blood, an acoustical measurement of the erythrocyte aggregation level can be obtained by analyzing the frequency dependence of ultrasonic backscattering from blood. However, the relation that exists among the variables describing the aggregation level and the backscattering coefficient needs to be better clarified. To achieve this purpose, a three-dimensional random model, the Neyman–Scott point process, is proposed to simulate red cell clustering in aggregative conditions at a low hematocrit (H<5%). The frequency dependence of the backscattering coefficient of blood, in non-Rayleigh conditions, is analytically derived from the model, as a function of the size distribution of the aggregates and of their mass fractal dimension. Quantitative predictions of the backscatter increase due to red cell aggregation are given. The parametric model of backscatter enables two descriptive indices of red cell aggregation to be extracted from experimental data, the packing factor W and the size factor Δ. Previously published backscatter measurements from porcine whole blood at 4.5% hematocrit, in the frequency range of 3.5 MHz–12.5 MHz, are used to study the shear-rate dependence of these two indices.
Adult and infant perception of two English phones
Authors: Pegg Judith E. , Werker Janet F.
Published: July 2002

Previous research has shown that young infants easily discriminate both native and non-native consonant contrasts, but by 10–12 months of age infants perform like adults and easily discriminate only native consonant contrasts. The present study was designed to determine what kind of experience is required to maintain discrimination of native consonants. To address this question, English listeners of three ages (6–8 months, 10–12 months, and adults) were presented with the phonetic difference, [d̥a] vs [t=a]. This distinction occurs in English but is not phonemic: [t=a] occurs when it follows an [s] (as in /sta/). If passive exposure is sufficient to maintain discrimination, all age groups should discriminate [d̥a] vs [t=a]. However, if phonological status plays a role, then older infants and adults should fail. In experiment 1, English adults judged [d̥a] and [t=a] to be equally good instances of the same phonemic category /da/. In an AX procedure in experiment 2, English adults discriminated [d̥a] vs [t=a] better than chance but worse than native phonemic levels. In the Conditioned Head Turn procedure in experiment 3, adults and 6- to 8-month-old infants discriminated [d̥a] vs [t=a], but 10- to 12-month-old infants did not. Taken together, these results are most consistent with the hypothesis that phonological status plays a role in maintaining discrimination of phonetic information.
Sound absorption in concert halls by seats, occupied and unoccupied, and by the hall’s interior surfaces
Authors: Beranek Leo L. , Hidaka Takayuki
Published: July 2002

From experimental data in concert and opera halls, absorption coefficients were determined for audience seating, unoccupied and occupied, of different constructions, and for gypsum, wood, plaster, and concrete interior surfaces of various thicknesses and densities. A total of ten halls were involved in the bare hall (before seats were installed) analysis, yielding “residual” absorption coefficients, i.e., coefficients for those areas not including the areas to be covered by the seating. In ten halls reverberation times were measured after installation of the seats (unoccupied) and in seven of these halls at concerts with seats fully occupied. The seating absorption coefficients are presented for “acoustical” audience areas, i.e., with a 0.5-m-wide edge around each seating block. The results are compared with the data of Appendix 5 in Beranek [Concert and Opera Halls: How They Sound (Acoustical Society of America, Woodbury, NY, 1996)]. The sound absorption data presented for interior surfaces and audience areas should permit more accurate estimation of reverberation times as a function of frequency for large halls during the planning stage.
Excitation and propagation of surface waves on a viscoelastic half-space with application to medical diagnosis
Authors: Royston T. J. , Mansy H. A. , Sandler R. H.
Published: July 2002

An analytical solution is developed for the problem of surface wave generation on a linear viscoelastic half-space by a finite rigid circular disk located on the surface and oscillating normal to it. The solution is an incremental advancement of theoretical work reported in articles focused on seismology. Since the application of interest here is medical diagnostics, the solution is verified experimentally using a viscoelastic phantom with material properties comparable to biological soft tissue. Findings suggest that prior estimates in the literature of the shear viscosity in human soft tissue may not be accurate in the low audible frequency range. Measurement of wave motion on the skin surface caused by internal biological functions or external stimuli has been studied by a few researchers for rapid, nonintrusive diagnosis of a variety of specific medical ailments. It is hoped that the developments reported here will advance these techniques and also provide insight into related diagnostic methods, such as sonoelastic imaging and other methodologies that utilize disease-related variations in tissue shear elasticity or variations in density due to gaseous inclusions.
Evaluation of Risk of Bias in Neuroimaging-Based Artificial Intelligence Models for Psychiatric Diagnosis
Authors: Chen Zhiyi , Liu Xuerong , Yang Qingwu , Wang Yan-Jiang , Miao Kuan , Gong Zheng , Yu Yang , Leonov Artemiy , Liu Chunlei , Feng Zhengzhi , Chuan-Peng Hu
Published: March 2023

Importance

Neuroimaging-based artificial intelligence (AI) diagnostic models have proliferated in psychiatry. However, their clinical applicability and reporting quality (ie, feasibility) for clinical practice have not been systematically evaluated.

Objective

To systematically assess the risk of bias (ROB) and reporting quality of neuroimaging-based AI models for psychiatric diagnosis.

Evidence Review

PubMed was searched for peer-reviewed, full-length articles published between January 1, 1990, and March 16, 2022. Studies aimed at developing or validating neuroimaging-based AI models for clinical diagnosis of psychiatric disorders were included. Reference lists were further searched for suitable original studies. Data extraction followed the CHARMS (Checklist for Critical Appraisal and Data Extraction for Systematic Reviews of Prediction Modeling Studies) and PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines. A closed-loop cross-sequential design was used for quality control. The PROBAST (Prediction Model Risk of Bias Assessment Tool) and modified CLEAR (Checklist for Evaluation of Image-Based Artificial Intelligence Reports) benchmarks were used to systematically evaluate ROB and reporting quality.

Findings

A total of 517 studies presenting 555 AI models were included and evaluated. Of these models, 461 (83.1%; 95% CI, 80.0%-86.2%) were rated as having a high overall ROB based on the PROBAST. The ROB was particular high in the analysis domain, including inadequate sample size (398 of 555 models [71.7%; 95% CI, 68.0%-75.6%]), poor model performance examination (with 100% of models lacking calibration examination), and lack of handling data complexity (550 of 555 models [99.1%; 95% CI, 98.3%-99.9%]). None of the AI models was perceived to be applicable to clinical practices. Overall reporting completeness (ie, number of reported items/number of total items) for the AI models was 61.2% (95% CI, 60.6%-61.8%), and the completeness was poorest for the technical assessment domain with 39.9% (95% CI, 38.8%-41.1%).

Conclusions and Relevance

This systematic review found that the clinical applicability and feasibility of neuroimaging-based AI models for psychiatric diagnosis were challenged by a high ROB and poor reporting quality. Particularly in the analysis domain, ROB in AI diagnostic models should be addressed before clinical application.
Comparison of Reporting Race and Ethnicity in Medical Journals Before and After Implementation of Reporting Guidance, 2019-2022
Authors: Flanagin Annette , Cintron Miriam Y. , Christiansen Stacy L. , Frey Tracy , Gray Timothy , Lo Iris Y. , Lewis Roger J.
Published: March 2023

This cross-sectional study compares race and ethnicity reporting in 3 medical journals before and after implementation of updated guidance on the reporting of race and ethnicity in August 2021.
Association of Supplemental Nutrition Assistance Program Retailers With Child Food Insecurity During the COVID-19 Pandemic
Authors: Li Qingxiao , Zhao Shuoli , Çakır Metin , Yu Zhixiu
Published: March 2023

This cross-sectional study of US Department of Agriculture and census data examines differences in child food insecurity and changes in Supplemental Nutrition Assistance Program (SNAP) retailers before and after the start of the COVID-19 pandemic.
Association Between State Antibullying Policies and Suicidal Behaviors Among Lesbian, Gay, Bisexual, and Questioning Youth
Authors: Liang Yang , Rees Daniel I. , Sabia Joseph J. , Smiley Cooper
Published: March 2023

This case-control study uses data from the 2009-2017 Youth Risk Behavior Survey to explore the association between antibullying law adoption and changes in suicidal behaviors among lesbian, gay, bisexual, and questioning youth.
Effect of Inorganic Nanoparticles on Energy‐Storage Properties of P(VDF–HFP)‐Based Nanocomposites
Authors: Guo Yan , Zhou Di , Li Da , Zhao Weichen , Pang LiXia , Shi Zhongqi , Liu Wenfeng , Su Jinzhan , Zhou Tao , Sun Shikuan
Published: March 2023

Polyvinylidene fluoride (PVDF) and its copolymers have been widely used in polymer‐based film capacitors due to their relatively high permittivity and electrical displacement compared with other polymers. Herein, poly(vinylidene fluoride‐hexafluoropropylene) (P(VDF–HFP)) is selected as the polymer matrix, and 0.5 (Bi0.5Na0.5)TiO3–0.5(Sr0.85Sm0.1)TiO3 (BNT–SST) nanoparticles are added as the filler into the polymer to prepare BNT–SST/P(VDF–HFP) nanocomposites. The microstructure, electrical properties, mechanical properties, and energy‐storage properties of the nanocomposites are investigated. The addition of BNT–SST nanoparticles improves the dielectric characteristics and breakdown strength of the nanocomposites. Particularly, when the BNT–SST filler content is 0.7 vol%, the highest breakdown strength reaches 545 MV m−1, which is 1.3 times higher than pure P(VDF–HFP). In addition, the insulation and mechanical properties of BNT–SST/P(VDF–HFP) composite films are improved. The highest direct current resistivity and Young's modulus obtained by 0.7 vol% BNT–SST/P(VDF–HFP) nanocomposites are 6.8 × 1013 Ω cm and 1.94 GPa, respectively. More importantly, at 545 MV m−1, the energy‐storage density and efficiency of 0.7 vol% BNT–SST/P(VDF–HFP) composites are 19.07 J cm−2 and 67.01%, respectively, which are better than other polymer matrix composites. These findings suggest that the addition of inorganic nanoparticles has important research implications for improving the energy‐storage performance of polymer‐based film capacitors.
Structural and Functional Adaptive Artificial Bone: Materials, Fabrications, and Properties
Authors: Feng Pei , Zhao Rongyang , Tang Weiming , Yang Feng , Tian Haifeng , Peng Shuping , Pan Hao , Shuai Cijun
Published: March 2023

It is an urgent need that defect repair can develop from simple device fixation to living tissue reconstruction, from short life function replacement to permanent regeneration repair. At present, bone transplantation has become the second largest transplantation surgery after blood transfusion, and artificial bone transplantation generates great hope for the repair and treatment of bone defect. In order to repair bone defect, artificial bone must have good biological properties and sufficient mechanical properties, and it should also have the shape matching to bone defect site and the connected porous structure. For structures and properties requirements of artificial bone, in this review three major challenges faced by artificial bone transplantation are systemtically analyzed and current methods and strategies to address these issues are discussed: 1) the need for developing a type of bone scaffold material with both biological and mechanical properties, 2) the need for realizing the controllable fabrication of individual shape and multistage pore structure of bone scaffold, 3) the need for realizing the transformation from man‐made structure to biological structure. Besides, it summarizes the advantages and disadvantages of these methods and discusses the potential future directions of structural and functional adaptive artificial bone for bone defect regeneration.
Superhydrophilic All‐pH‐Adaptable Redox Conjugated Porous Polymers as Universal and Ultrarobust Ion Hosts for Diverse Energy Storage with Chemical Self‐Chargeability
Authors: Zhong Linfeng , Li Jing , Liu Cong , Fang Long , Yuan Zhongke , Yu Dingshan , Chen Xudong
Published: March 2023

Herein, a new fibrous conjugated microporous polymer bearing phenazine species (PNZ‐CMP) is reported as a universal and ultrastable electrode to host various mono‐ and multi‐valent charge carriers for diverse aqueous rechargeable cells combining rapid kinetics, ultralong lifespan, and chemical rechargeability. The porous cross‐linked structure, interconnected donor‐acceptor network, and readily accessible active sites endow PNZ‐CMP with highly‐reversible redox activity, superhydrophilicity, facile electron transport, high ion diffusion coefficient, and all‐pH‐adaptability (−1 to 15) in aqueous electrolytes. Thus, adopting PNZ‐CMP electrodes enables good compatibility with H+/Li+/Na+/K+/Zn2+/Al3+ ions and fast surface‐controlled redox reactions for diverse aqueous battery chemistry. Multiple PNZ‐CMP‐based full cells show superior electrochemical performance especially ultralong lifespan, e.g., ≈84% capacity retention over 200 days for K+, ≈100% over 127 days for Zn2+, and ≈76% over 47 days for anion‐coordinated Al ions, surpassing small molecule counterparts and most previously‐reported corresponding systems. The spontaneous redox chemistry of reduced phenazine species with O2 is first explored to render PNZ‐CMP with repeatable chemical self‐chargeability in four electrolytes. Especially in 0.05 m H2SO4, an accumulative discharge capacity up to 48505 mAh g−1 is achieved via facile self‐charging, which can originate from the “reactive antiaromaticity to stable aromaticity” conversion of the redox moieties as revealed by theoretical studies.
High‐Energy‐Density All‐Organic Dielectric Film via a Continuous Preparation Processing
Authors: Zhang Yang , Li Li , Li Xiaoyu , Feng Rui , Zhao Tingting , Pan Meng , Dong Lijie
Published: March 2023

Dielectric polymers with high power density and breakdown strength (Eb) are indispensably used in electrostatic energy‐storing systems and devices. However, the discharged energy density (Ue) of dielectric polymers is severely limited due to the relatively low dielectric constant (K). Although current polymer composites improve K, this approach usually faces challenges in enhancing Ue due to the trade‐off relation between K and Eb and difficulties in scalable production of dielectric films. Here, a fully melt‐extrudable, meter‐scale, and high‐Ue ferroelectric polymer‐based all organic composite film comprising a poly(p‐phenylene terephthalamide)‐based fluxible polymer (denoted as f‐PPTA) is reported. The polymer composite with only 2 wt% of f‐PPTA presents a productivity of 12 m2 h−1 and an ultrahigh Ue of 20.7 J cm−3, which outperforms other extruded dielectric polymers reported in the literatures. Such enhancements of dielectric and capacitive properties have been comprehensively investigated and attributed to the crystallization behavior modulations and conformation changes induced by f‐PPTA. As a demonstration of real applications, the dielectric capacitors established based on the extruded films enable tens of times higher efficacy on powering electronic devices than biaxially oriented polypropylene capacitors, in addition to long‐term cyclic stability. This study opens up new avenue for the design and fabrication of high‐Ue polymer dielectrics that are totally compatible with industrial production.
Targeting STING Activation by Antigen‐Inspired MnO2 Nanovaccines Optimizes Tumor Radiotherapy
Authors: Gu Yuan , Lin Subin , Wu Yanxian , Xu Pei , Zhu Wen , Wang Yangyun , Cheng Xiaju , Zhang Leshuai W. , Stauber Roland H. , Wang Yong , Gao Mingyuan
Published: March 2023

Immune checkpoint blockers therapy can improve the radiotherapy‐induced immunosuppression by enhancing interferon secretion, but still suffer from low clinical response rate and potential adverse effects. Mn2+‐mediated activation of interferon gene stimulator (STING) pathway provides an alternative for combination radioimmunotherapy of tumor. However, it is still a challenge for specific delivery of Mn2+ to innate immune cells and targeting activation of STING pathway. Herein, a novel antigen‐inspired MnO2 nanovaccine is fabricated as Mn2+ source and functionalized with mannose, enabling it to target innate immune cells to activate the STING pathway. Meanwhile, the release of Mn2+ in the intracellular lysosomes can also be for magnetic resonance imaging to monitor the dynamic distribution of nanovaccines in vivo. The targeting activation of STING pathway can enhance radiotherapy‐induced immune responses for inhibiting local and distant tumors, and resisting tumor metastasis. The study proposes an optimized radiotherapy strategy through targeting STING activation of antigen‐inspired nanovaccines.