bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational Mechanics of Dry Friction and Impact Systems
Authors: Blekhman Iliya I.
Published: February 2021

The method of direct separation of motions and the general approach, called by the author “vibrational mechanics”, is developed so as to fit the problems of the effect of vibration on systems with dry friction and shock. The main idea of this approach lies in the transfer from the initial system of differential equations to the system, describing only the slow components of motion, most interesting for applications. It is these equations that are called the equations of vibrational mechanics. The advantages of this approach are especially significant in the case of systems with dry friction (Coulomb friction) and with unilateral constraints whose presence in case of vibration leads to multiple collisions of the system bodies. Instead of the not smooth system or with the discontinuous right sides there is a “smooth” system often of a lower order; an essentially non-potential system may be answered by a potential system.

Methods and approaches presented in the report are illustrated by the solution of two applied problems — a simplest problem of the transportation of a body along a rough vibrating surface and a problem on the motion of a body in space between the vibrating surfaces under periodic impacts. A short reference of investigations is given where the proposed approach is used or can be used quite effectively. In conclusion the main regularity is formulated which characterizes the action of vibration on systems with dry friction and impacts.
Mechanical Systems With Impacts: Comparison of Several Numerical Methods
Authors: Lamarque C. H. , Janin O.
Published: February 2021

We study the performances of several numerical methods (Paoli-Schatzman, Newmark, Runge-Kutta) in order to compute periodic behavior of a simple one-degree-of-freedom impacting oscillator. Some theoretical results are given and numerical tests are performed. We compare mathematical and numerical results using our simple example exhibiting either finite or infinite number of impacts per period. Comparison of exact and numerical solution provides a practical order for each scheme. We conclude about the use of the different numerical methods.
Tribometer for Dry Friction Measurement
Authors: Brandl Marc , Pfeiffer Friedrich
Published: February 2021

This paper deals with the measurement of dry friction. A tribometer was developed in order to identify both the sticking and the sliding coefficient of friction. The aim was to determine the so called Stribeck-curve of any material in contact. The design of the plant is presented. Avoiding errors in recalculating the coefficient of friction, a detailed model of the plant as a multi body system with motor feedback was generated. Advantages of the tribometer are shown in simulations. Some results of measurements in comparison with simulation results are presented.
Dynamic Analysis of Human Walking: Treadmills, Loss of Sensation, and Comparisons With Surrogate Data
Authors: Dingwell Jonathan B. , Cavanagh Peter R. , Sternad Dagmar
Published: February 2021

Correlation dimensions and average maximum finite-time Lyapunov (MFTL) exponents were used to examine the kinematics of continuous level walking in human subjects. Comparisons were made between overground (OG) and motorized treadmill (TM) walking in young healthy subjects and between diabetic neuropathic (NP) patients and healthy controls (CO) during overground walking. Surrogate data were used to examine the stochastic nature of the stride-to-stride variability seen in these walking patterns. There were three primary results. First, the motorized treadmill significantly constrained the neuromuscular control and normal movement kinematics of walking. Second, NP patients demonstrated greater correlation dimensions in their movement patterns and slowed their walking speeds to maintain maximum upper body stability during unrestricted walking over level ground. Third, stride-to-stride fluctuations in walking kinematics could be clearly distinguished from correlated Gaussian noise and demonstrated changes in their structure that were related to the loss of peripheral sensation.
Nonlinear Systems for Distances and Displacements Measurement
Authors: Mozuras Almantas , Kontvainaite Asta
Published: February 2021

In conventional methods, a physical system is considered more suitable for measurement purposes the greater its linearity is. However, purely linear converting systems are not available. The use of the linear features in the measurement process causes the drawbacks: systematic error due to nonlinear distortions, low signal-to-noise ratio, low measurement range, necessity to evaluate a great number of a priori parameters in order to obtain an absolute result, and low thermal stability because every a priori parameter itself has a temperature dependence. To exclude these drawbacks a method has been developed using nonlinearities in the base of displacements measuring process. The method is implemented using electretic, electrostatic, and photoelectric transducers. The contactless transducer is placed parallel to the surface of the object which displacements are measured. The transducer is driven to harmonic oscillations. Typical time intervals of the coded signal are measured. The object displacements are determined according to the changes of the typical time intervals. The method itself has no errors because approximations have been not made while deriving the relations. The source of errors is inaccurate registration of the start and end of the typical time intervals. The measurement is possible only if the physical system is nonlinear. The results of experimental investigations confirm the theoretical conclusions. The method allows one to increase measurement range significantly (for example, measurement range of the conventional capacitance meters is ∼10−2mm and in the proposed method measurement range using capacitance converter is about 1 mm).
Detection of Low-SNR Signals Using Dynamical Models Estimated With Higher-Order Data Moments
Authors: Péntek Áron , Kadtke James B.
Published: February 2021

We discuss a method for estimating nonlinear dynamical models from data, to construct a closed-form, few-parameter representation. The model coefficients are estimated using a Yule-Walker type equation involving higher-order correlations, which provides computational speed, numerical stability and noise robustness. We implement a multi-feature detector based on Mahalanobis distance and compute ROC curves for several signal classes. We show that the dynamical detectors’ performance can be improved significantly by increasing the sampling rate.
Nonlinear Dynamical Modeling of Sonar Signal Propagation
Authors: Katz Richard A. , Quazi Azizul H.
Published: February 2021

Sonar signal propagation has been traditionally modeled as a linear stochastic process. This research is a major departure from that classical viewpoint and is aimed at modeling acoustic signal propagation dynamics deterministically using the analysis tools of Nonlinear Dynamics and Chaos Theory. Advantages of using this new paradigm over traditional approaches to sonar modeling are demonstrated by simulating a linear frequency modulated (LFM) active sonar signal and two nonlinear variations of it. When nonlinear performance metrics called the mutual information (MI) and the differential radius (DR) are applied to both linear and nonlinear variants of the LFM signal, both metrics are found to be useful detectors of nonlinearity in a simulated acoustic time series. Next we demonstrate the DR technique, on real ultrasonic time series data, that was found to be useful for the diagnosis and treatment of a heart disease called atrial fibrillation. After summarizing results, we conclude with recommended future directions in applied nonlinear sonar signal propagation research.
Damage Detection in Rods Using Wave Propagation and Regression Analysis
Authors: Feroz K. T. , Oyadiji S. O.
Published: February 2021

The phenomena of wave propagation in rods was studied both numerically and experimentally. The finite element (FE) code ABAQUS was used for the numerical study while PZT (lead zirconium titanate) sensors and a 50 MHz transient recorder were used experimentally to monitor and to capture the propagation of stress pulses. For the study of damage detection in the rods the analyses and the experiments were repeated by introducing slots in a fixed axial location of the rod. A longitudinal wave was induced in the rod via collinear impact which was modelled in the FE analyses using the force-time history computed from the classical Hertz contact theory. In the experimental measurements this was achieved by a spherical ball impact at one plane end of the rods. It is shown that the predicted and measured strain-time histories for the defect-free rod and for the rods with defect correlate quite well. These results also show that defects can be located using the wave propagation phenomena. A regression analysis technique of the predicted and measured strain histories of the defect free rod and of the rod with defect was also performed. The results show that this technique is more efficient for smaller defects. In particular, it is shown that the area enclosed by the regression curve increases as the defect size increases.
Identification of a Nonlinear Vibration System Using Simulated Annealing, Genetic Algorithm and Programming
Authors: Sláma Lubomir , Balátě Mojmir , Krejsa Jiří , Slavík Jan
Published: February 2021

Application of genetic algorithm and genetic programming to identification of a nonlinear vibration system is presented. Both the theoretical groundwork and experimental results are included. The genetic algorithm is used for identification of parameters of nonlinear stiffness and friction damping characteristics of a single-degree-of-freedom model of a vibration isolation system. The genetic programming is used for identification of a functional form and parameters of a load-deflection characteristic of a rubber isolator. Obtained results from computational experiments are presented and discussed. Results of GA are compared to results obtained by using a simulated annealing method.
Design of Reduced Order H∞ Controller for Smart Structures
Authors: Moreira Fernando J. O. , Arruda José Roberto de França , Inman Daniel J.
Published: February 2021

In this paper the design of a low order controller for a high-order, smart structural system is presented. The application considered here is a model of a solar panel dynamically similar to those used on satellites. Smart structure refers here to the use of integrated piezoceramic materials as sensors and actuators in the structural system in order to implement the control. The theoretical contribution is made be extending well known robust control theory by relating the high frequency robustness condition to the residual uncertainty, removing a trial and error step in the normal robust control design. The procedure is applied experimentally to a one-meter long frame that is coupled in bending and torsion. Both numerical and experimental results are given.
Vibrations Analysis for Gun Systems by Multibody Dynamics
Authors: Wang Deshi , Xiao Renbin , Ouyang Guangyao
Published: February 2021

The multi-rigid-bodies model for the single barrel gun has been developed and the structure vibration of the gun has been analyzed though Lagrangian equations reduced by the software on microcomputer. It is shown that the deck stiffness is significant in the effect of the gun vibration, and then that design of a suitable equilibrium equipment and design of the elastic connection axle to increasing the flexibility in pitching movement can effectively decrease the vibration amplitudes of the tube end. The maximum amplitude, for example, could decay to ten percent of that when the measures mentioned above are adopted. It also indicates that entirely removing the vibration is impossible except relevant vibration absorbing measures are adopted. The method and results are also significant in checking the motions of the mechanisms designed in the guns.
Some Ideas on the Local Control of Nonlinear Systems With Time-Periodic Coefficients
Authors: Dávid Alexandra , Sinha S. C.
Published: February 2021

In this paper ideas on local control of linear and nonlinear time-periodic systems are presented. Our first goal is to stabilize the system far away from bifurcation points. In this case, the classical linear state feedback stabilization based on pole placement is generalized such that it is applicable to time-periodic systems. The linear state-feedback controller design involves computation of the fundamental solution matrix of the system in a symbolic form as function of the control parameters.

Next, we focus on the bifurcation control of time-periodic systems. When the linearized system is in a critical case of stability (i.e. when it has Floquet multipliers on the unit circle of the complex plane) and the critical modes are uncontrollable in the linear sense, then a purely nonlinear state-feedback controller is designed to stabilize the equilibrium at the bifurcation point and ensure the stability of the bifurcated nontrivial solution. When the linearized system is linearly controllable, then it is shown that an appropriately chosen linear state-feedback control can also modify the nonlinear features of the bifurcations, such as stability or size of the limit cycles or quasi-periodic limit sets. The control techniques are based on a series of transformations that convert the system into a time-invariant form. First, the Lyapunov-Floquet transformation is used to make the linear part of the periodic system time-invariant. Then, time-periodic center manifold reduction and time-dependent normal form theory are applied to obtain the simplest nonlinear form of a system undergoing bifurcation. For most codimension one bifurcations the normal form is completely time-invariant and therefore, it is a rather simple task to choose the appropriate control gains. These ideas are illustrated by an example of a parametrically excited simple pendulum undergoing symmetry breaking bifurcation.
Parametric Instability of a Leipholz Column Under Periodic Excitation
Authors: Kang Bongsu , Tan Chin An
Published: February 2021

In this paper, the parametric instability of a Leipholz column under four boundary conditions is studied. The distributed, follower-type axial load is assumed to be uniform and periodic. Instability regions are obtained and the existence of combination resonance of sum and difference types is discussed for each set of boundary conditions. It is found that combination resonance of sum type exists in all the cases of boundary conditions considered, but the difference type exists only in the cases of clamped-simply supported and clamped-free boundary conditions. The combination resonance is shown to be as important as the simple parametric resonance. Results, when compared to a column under a periodic end load, show that the instability characteristics of these two columns are considerably different.
Nonlinear Shape Control of Shells and Plates
Authors: Tzou H. S. , Bao Y. , Chou C. S.
Published: February 2021

Adaptive shape control is essential in many high-performance engineering systems, such as nozzles, airplane wings, helicopter blades, etc. Recent development of smart structures and structronic systems offers new alternatives to shape control with inherent and embedded actuator components. Imposed shape control often involves large deformations implying that the conventional linear theory is no longer applicable. This study is to explore a new structural control concept based on nonlinear theories. Nonlinear piezoelectric shell equations are derived based on von Karman geometric nonlinearity. Physical significance and application are discussed. As to compare the linear and nonlinear theories, a zero-curvature shell–plate is investigated. Analytical results suggest that the linear theory is indeed invalid when large deformation shape control is considered. Differences between the two theories are presented. Control effects of the plate with polymeric and ceramic piezoelectric actuators are compared.
Reduction of Noise Inside a Cavity by Piezoelectric Actuators
Authors: Hagiwara Ichiro , Rao Zhushi , Shi Qinzhong
Published: February 2021

A new analytical model is developed for the reduction of noise inside a cavity using distributed piezoelectric actuators. The cavity is modeled with four rigid walls and two flexible panels, panel on the top is excited by disturbing point forces and thus radiating structure borne noise into the cavity, and the other panel which is on the bottom is bonded with actuators to control the noise inside the cavity. Modal coupling method is used to establish the governing equations of motion of the fully coupled acoustics-structure-piezoelectric patch system. Two performance functions relating ‘global’ and ‘local’ optimal control of sound pressure levels (SPL) respectively are applied to obtain the control laws. Numerical investigations into the effect of number of actuators, error sensors as well as disturbing point forces on SPL’s are presented. Based on the studies, it is found that the number of actuators has a significant influence on SPL’s for local control case, while for global control case, this influence is quite limited. The discussions on associated control mechanism show that both the mechanisms of modal amplitude suppression and modal rearrangement may sometimes coexist in the implementation of optimal noise control.
Benchmark Problems for the Analysis of Piezoelectric Controlled Smart Structures
Authors: Gabbert U. , Görnandt A. , Köppe H. , Seeger F.
Published: February 2021

In the paper at first the theoretical basis for the simulation of piezothermoelastic smart structures is discussed briefly. Then an overview about our finite element simulation tool for smart structures is given. During the development of this analysis tool several test examples have been solved and compared with theoretical results from the literature as well as experimental results. During this process of software verification and qualification we were tackled with several problems, such as incomplete and incorrect data from literature, especially missing material data, incorrect boundary and load conditions, etc. Consequently, a collection of well documented benchmark examples should be created for smart structures. The selection of suited examples should follow the guidelines of the well established NAFEMS benchmarks in other fields of mechanics. In the paper a first collection of some smart structures benchmark problems is proposed and discussed.
A New Integrated Algorithm of Structure Determination and Parameter Estimation for Nonlinear Systems Identification
Authors: Wang Wang Xiao , Xie Jianyin
Published: February 2021

A new integrated algorithm of structure determination and parameter estimation is proposed for nonlinear systems identification in this paper, which is based on the Householder Transformation (HT), Givens and Modified Gram-Schmidt (MGS) algorithms. While being used for the polynomial and rational NARMAX model identification, it can select the model terms while deleting the unimportant ones from the assumed full model, avoiding the storage difficulty as the CGS identification algorithm does which is proposed by Billings et. al., and is numerically more stable. Combining the H algorithm with the modified bidiagonalization least squares (MBLS) algorithm and the singular value decomposition (SVD) method respectively, two algorithms referred to as the MBLSHT and SVDHT ones are proposed for the polynomial and rational NARMAX model identification. They are all numerically more stable than the HT or Givens or MGS algorithm given in this paper, and the MBLSHT algorithm has the best performance. A higher precision for the parameter estimation can thus be obtained by them, as supported b simulation results.
Joint Design and Application of Adaptive Filter and Optimal Control
Authors: Ren Yu Hong , Jing Zhong Liang
Published: February 2021

Kaiman filter is well suited for application to the problems of missile guidance and control. In this paper, we make use of the Kaiman filter theory to develop an efficient scheme for estimating the current states of maneuvering targets, and optimal guidance law is applied in order for a high performance index of miss distance. This scheme is designed to suit for tracking several types of target if aircraft can not provide much known information regarding maneuvering targets before launching missile. It is shown how an adaptive filter based on Current Statistical Model can be applied in conjunction with the optimal guidance law to improve system attacking performance and to relax the requirements of maneuvering target acceleration information during tracking and attacking.
Air-to-Air Attack Based Performance Analysis of Integrated Avionics Systems
Authors: Xu Yi , Jing Zhongliang , Jin Dekun
Published: February 2021

This paper proposes the advanced techniques used by Integrated Avionics System to track and attack the maneuvering target effectively, develops the parameter sensitivity analysis, and then point out the primary factors and the secondary factors affecting the attack effectiveness. First of all, mathematical models are provided, including the kinematic model, the airborne radar tracking model, the fire control model, the pilot-manipulation model and the fire logic. With the use of self-adaptive Kaiman filter, the algorithm for the maneuvering target tracking is suggested. By means of the forced singular perturbation, the suboptimal strategy for three-dimensional pursuit-evasion differential game problem is developed. Secondly, based on the models, the algorithm and the strategy above, the simulation flow chart is proposed, which is in accordance with the actual air-to-air attack. Thirdly, in the light of the relative sensibility function, the values of system parameter sensibility about several parameters are calculated. Fourthly, appropriate parameter selections for improving and updating the attack capability are suggested. Finally, the imaginary air-to-air scenario is simulated to analyze the performance of Integrated Avionics System. The simulation results show that the system can track the maneuvering target reliably and attack it accurately with the longer locking time, and the burden of numerical calculation is lightened considerably.
Application of a Five-Axis Robot Manipulator to Maintenance Operations
Authors: Lacagnina Michele , Petrone Francesco , Sinatra Rosario
Published: February 2021

This paper describes the application of a five-axis manipulator with a particular architecture containing only revolute joints to the performance of maintenance operations on the concrete spire of the “Madonna delle Lacrime” church, in Siracusa, Italy. The kinematics model is derived and a computation of the joint coordinates and their time rates are calculated by the least-squares approximation, as proposed by Angeles. The Newton-Eulero algorithm is implemented for a simulation of the inverse dynamics of a not-simple trajectory in Cartesian space required to perform the maintenance task.
Material properties and performance of ErAs:In(Al)GaAs photoconductors for 1550 nm laser operation
Authors: Nandi U. , Mohammadi M. , Lu H. , Norman J. , Gossard A. C. , Alff L. , Preu S.
Published: February 2021

ErAs:In(Al)GaAs photoconductors have proven to be outstanding devices for photonic terahertz (0.1–10 THz) generation and detection with previously reported sub-0.5 ps carrier lifetimes. We present the so far most detailed material characterization of these superlattices composed of ErAs, InGaAs, and InAlAs layers grown by molecular beam epitaxy. The variation of the material properties as a function of the ErAs concentration and the superlattice structure is discussed with focus on source materials. Infrared spectroscopy shows an absorption coefficient in the range of 4700–6600 cm−1 at 1550 nm, with shallow absorption edges toward longer wavelengths caused by absorption of ErAs precipitates. IV characterization and Hall measurements show that samples with only 0.8 monolayers of electrically compensated ErAs precipitates (p-delta-doped at 5×1013 cm−2) and aluminum-containing spacer layers enable high dark resistance (∼10–20 MΩ) and high breakdown field strengths beyond 100 kV/cm, corresponding to >500 V for a 50 μm gap. With higher ErAs concentration of 1.6 ML (2.4 ML), the resistance decreases by a factor of ∼40 (120) for an otherwise identical superlattice structure. We propose a theoretical model for calculation of the excess current generated due to heating and for the estimation of the photocurrent from the total illuminated current. The paper concludes with terahertz time-domain spectroscopy measurements demonstrating the strengths of the material system and validating the proposed model.
Racing and Training Physiology of an Elite Ultra-Endurance Cyclist: Case Study of 2 Record-Setting Performances
Authors: Rothschild Jeffrey A. , Delcourt Matthieu , Maunder Ed , Plews Daniel J.
Published: February 2021

Purpose: To present a case report of an elite ultra-endurance cyclist, who was the winner and course record holder of 2 distinct races within a 4-month span: a 24-hour solo cycling race and a 2-man team multiday race (Race Across America). Methods: The athlete’s raw data (cycling power, heart rate [HR], speed, and distance) were obtained and analyzed for 2 ultra-endurance races and 11 weeks of training in between. Results: For the 24-hour race, the athlete completed 861.6 km (average speed 35.9 km·h−1, average power 210 W [2.8 W·kg−1], average HR 121 beats per minute) with a 37% decrease in power and a 22% decrease in HR throughout the race. During the 11 weeks between the 24-hour race and Race Across America, training intensity distribution (Zone 1/2/3) based on HR was 51%/39%/10%. For the Race Across America, total team time to complete the 4939-km race was 6 days, 10 hours, 39 minutes, at an average speed of 31.9 km·h−1. Of this, the athlete featured in this case study rode 75.2 hours, completing 2532 km (average speed 33.7 km·h−1, average power 203 W [2.7 W·kg−1]), with a 12% decrease in power throughout the race. Power during daytime segments was greater than nighttime (212 [25] vs 189 [18] W, P < .001, ). Conclusions: This case report highlights the performance requirements of elite ultra-endurance cycling. Although average power was similar when riding for 24 hours continuously and 75 hours intermittently over 6.5 days, there were large differences in pacing strategies and within-day power-output changes.
Pooled Versus Individualized Load–Velocity Profiling in the Free-Weight Back Squat and Power Clean
Authors: Thompson Steve W. , Rogerson David , Ruddock Alan , Banyard Harry G. , Barnes Andrew
Published: February 2021

Purpose: This study compared pooled against individualized load–velocity profiles (LVPs) in the free-weight back squat and power clean. Methods: A total of 10 competitive weightlifters completed baseline 1-repetition maximum assessments in the back squat and power clean. Three incremental LVPs were completed, separated by 48 to 72 hours. Mean and peak velocity were measured via a linear-position transducer (GymAware). Linear and nonlinear (second-order polynomial) regression models were applied to all pooled and individualized LVP data. A combination of coefficient of variation (CV), intraclass correlation coefficient, typical error of measurement, and limits of agreement assessed between-subject variability and within-subject reliability. Acceptable reliability was defined a priori as intraclass correlation coefficient > .7 and CV < 10%. Results: Very high to practically perfect inverse relationships were evident in the back squat (r = .83–.96) and power clean (r = .83–.89) for both regression models; however, stronger correlations were observed in the individualized LVPs for both exercises (r = .85–.99). Between-subject variability was moderate to large across all relative loads in the back squat (CV = 8.2%–27.8%) but smaller in the power clean (CV = 4.6%–8.5%). The power clean met our criteria for acceptable reliability across all relative loads; however, the back squat revealed large CVs in loads ≥90% of 1-repetition maximum (13.1%–20.5%). Conclusions: Evidently, load–velocity characteristics are highly individualized, with acceptable levels of reliability observed in the power clean but not in the back squat (≥90% of 1-repetition maximum). If practitioners want to adopt load–velocity profiling as part of their testing and monitoring procedures, an individualized LVP should be utilized over pooled LVPs.
Inherited lithospheric structures control arc-continent collisional heterogeneity
Authors: Miller M.S. , Zhang P. , Dahlquist M.P. , West A.J. , Becker T.W. , Harris C.W.
Published: February 2021

From west to east along the Sunda-Banda arc, convergence of the Indo-Australian plate transitions from subduction of oceanic lithosphere to arc-continent collision. This region of eastern Indonesia and Timor-Leste provides an opportunity for unraveling the processes that occur during collision between a continent and a volcanic arc, and it can be viewed as the temporal transition of this process along strike. We collected a range of complementary geological and geophysical data to place constraints on the geometry and history of arc-continent collision. Utilizing ∼4 yr of new broadband seismic data, we imaged the structure of the crust through the uppermost mantle. Ambient noise tomography shows velocity anomalies along strike and across the arc that are attributed to the inherited structure of the incoming and colliding Australian plate. The pattern of anomalies at depth resembles the system of salients and embayments that is present offshore western Australia, which formed during rifting of east Gondwana. Previously identified changes in geochemistry of volcanics from Pb isotope anomalies from the inner arc islands correlate with newly identified velocity structures representing the underthrusted and subducted Indo-Australian plate. Reconstruction of uplift from river profiles from the outer arc islands suggests rapid uplift at the ends of the islands of Timor and western Sumba, which coincide with the edges of the volcanic-margin protrusions as inferred from the tomography. These findings suggest that the tectonic evolution of this region is defined by inherited structure of the Gondwana rifted continental margin of the incoming plate. Therefore, the initial template of plate structure controls orogenesis.
Biomineralization of the Cambrian chancelloriids
Authors: Yun Hao , Zhang Xingliang , Brock Glenn A. , Li Luoyang , Li Guoxiang
Published: February 2021

As extinct animals that flourished during the Cambrian explosion, chancelloriids have a unique body plan lacking guts but with a flexible integument and a suite of star-shaped, hollow sclerites. Due to this body plan, along with the paucity of knowledge on sclerite biomineralization, the phylogenetic position of chancelloriids within the Metazoa is still controversial. Integration of analyses of diverse fossils from Cambrian stage 2 to the Wuliuan Stage of China and Australia indicates that chancelloriid sclerites possess an encasement-like organic layer and a fibrous aragonitic layer. The organic layer is inferred to be a specialized trait derived from the epidermal integument of the animal body. The sclerites were likely biomineralized by using the outer organic layer as a template to absorb cations and precipitate crystal nuclei, reflecting a strategy adopted by a range of eumetazoans with a developed epidermis. Therefore, the hypothesis that chancelloriids represent an epitheliozoan-grade animal and an early explorer of template-based biomineralization is supported.
Wide-blocky veins explained by dependency of crystal growth rate on fracture surface type: Insights from phase-field modeling
Authors: Spruženiece Liene , Späth Michael , Urai Janos L. , Ukar Estibalitz , Selzer Michael , Nestler Britta
Published: February 2021

Vein microstructures contain a wealth of information on coupled chemical and mechanical processes of fracturing, fluid transport, and crystal growth. Numerical simulations have been used for exploring the factors controlling the development of vein microstructures; however, they have not been quantitatively validated against natural veins. Here we combined phase-field modeling with microtextural analysis of previously unexplained wide-blocky calcite veins in natural limestone and of the fresh fracture surface in this limestone. Results show that the wide-blocky vein textures can only be reproduced if ∼10%–20% of crystals grow faster than the rest. This fraction corresponds to the amount of transgranularly broken grains that were observed on the experimental fracture surfaces, which are dominantly intergranular. We hypothesize that transgranular fractures allow faster growth of vein minerals due to the lack of clay coatings and other nucleation discontinuities that are common along intergranular cracks. Our simulation results show remarkable similarity to the natural veins and reproduce the nonlinear relationship between vein crystal width and vein aperture. This allows accurate simulations of crystal growth processes and related permeability evolution in fractured rocks.
Gulf of Aden spreading does not conform to triple-junction formation
Authors: Almalki Khalid A. , Betts Peter G.
Published: February 2021

The Gulf of Aden represents an evolving example of a juvenile ocean system and is considered the most evolved rift arm of the Afar triple junction. We have undertaken analysis of recent coupled satellite and marine potential-field data to understand the first-order crustal architecture along the entire length of the gulf. Our interpretation suggests the Gulf of Aden has three domains with distinct free-air gravity and magnetic characteristics. These domains record a progression from active seafloor spreading in the eastern domain, through isolated and discontinuous spreading segments in the central domain, to active continental rifting in the western domain immediately adjacent to the Afar triple junction. Forward models suggest the presence of transitional crust, which displays linear magnetic stripe–like anomalies that bound oceanic stripes in the central domain and covering the majority of the western domain. Magnetic anomalies differ from magnetic stripes sensu stricto because they are discontinuous and cannot be correlated along the length of the gulf. Detection of northwest-southeast extension in the central domain based on magnetic stripe orientation is inconsistent with the regional northeast-southwest extension. Our observations reflect heterogeneous opening of the Gulf of Aden basins, in which spreading is migrating toward Afar as a series of isolated spreading segments, rather than initiating at the junction as proposed by classical plate-tectonic theory. This mechanism of ocean initiation is inconsistent with transtensional models that involve wholesale tearing of continental crust and contradicts conceptual models that rely on the Afar plume in initiating or driving the extension.
Detrital zircon petrochronology of central Australia, and implications for the secular record of zircon trace element composition
Authors: Verdel Charles , Campbell Matthew J. , Allen Charlotte M.
Published: February 2021

Hafnium (Hf) isotope composition of zircon has been integrated with U-Pb age to form a long-term (>4 b.y.) record of the evolution of the crust. In contrast, trace element compositions of zircon are most commonly utilized in local- or regional-scale petrological studies, and the most noteworthy applications of trace element studies of detrital zircon have been in “fingerprinting” potential source lithologies. The extent to which zircon trace element compositions varied globally over geological time scales (as, for example, zircon U-Pb age abundance, O isotope composition, and Hf isotope composition seem to have varied) has been little explored, and it is a topic that is well suited to the large data sets produced by detrital zircon studies. In this study we present new detrital zircon U-Pb ages and trace element compositions from a continent-scale basin system in Australia (the Centralian Superbasin) that bear directly on the Proterozoic history of Australia and which may be applicable to broader interpretations of plate-tectonic processes in other regions. U-Pb ages of detrital zircon in the Centralian Superbasin are dominated by populations of ca. 1800, 1600, 1200, and 600 Ma, and secular variations of zircon Hf isotope ratios are correlated with some trace element parameters between these major age populations. In particular, elevated εHf(i) (i.e., radiogenic “juvenile” Hf isotope composition) of detrital zircon in the Centralian Superbasin tends to correspond with relatively high values of Yb/U, Ce anomaly, and Lu/Nd (i.e., depletion of light rare earth elements). These correlations seem to be fundamentally governed by three related factors: elemental compatibility in the continental crust versus mantle, the thickness of continental crust, and the contributions of sediment to magmas. Similar trace element versus εHf(i) patterns among a global zircon data set suggest broad applicability. One particularly intriguing aspect of the global zircon data set is a late Neoproterozoic to Cambrian period during which both zircon εHf(i) and Yb/U reached minima, marking an era of anomalous zircon geochemistry that was related to significant contributions from old continental crust.
Along-strike variations in protothrust zone characteristics at the Nankai Trough subduction margin
Authors: Tilley Hannah L. , Moore Gregory F. , Yamashita Mikiya , Kodaira Shuichi
Published: February 2021

Significant along-strike changes in the protothrust zone at the toe of the Nankai Trough accretionary prism were imaged in new high-resolution seismic reflection data. The width of the protothrust zone varies greatly along strike; two spatially discrete segments have a wide protothrust zone (∼3.3–7.8 km, ∼50–110 protothrusts), and two segments have almost no protothrust zone (∼0.5–2.8 km, <20 protothrusts). The widest protothrust zone occurs in the region with the widest and thickest sediment wedge and subducting turbidite package, both of which are influenced by basement topography. The trench wedge size and lithology, the lithology of the subducting section, and the basement topography all influence the rate of consolidation in the trench wedge, which we hypothesize is an important control over the presence and width of the protothrust zone. We conclude that protothrusts are fractures that form from shear surfaces in deformation band clusters as the trench fill sediment is consolidated. Strain localization occurs at sites with a high density of protothrusts, which become the probable locations of future frontal thrust propagation. The frontal thrust may propagate forward with a lower buildup of strain where it is adjacent to a wide protothrust zone than at areas with a narrow or no protothrust zone. This is reflected in the accretionary prism geometry, where wide protothrust zones occur adjacent to fault-propagation folds with shallow prism toe surface slopes.
Emergence and Evolution of Barbados
Authors: Speed Robert C. , Cheng Hai
Published: February 2021

Emergence and Evolution of Barbados is a three-part analysis of the Quaternary geologic and geomorphologic evolution of the island of Barbados in the southeastern Caribbean. “Geology of Southeastern Barbados” assembles and integrates detailed observations into a complex 700 k.y. history of marine sculpting and riverine flooding processes. “Marine Terrace Evolution of Windward Barbados” revises the Quaternary stratigraphy of the island, describes the tectonics of emergence, and demonstrates that uplift rates vary by location. “Active Emergence, Chronology, and Limestone Facies in Southeastern Windward Barbados” is the first comprehensive study to integrate marine erosion and deposition with tectonic uplift rates. Major findings of this work are that Barbados’ Central Highlands are an erosional remnant, and that terraces originated principally by marine erosion rather than by reef construction.
Changing clinical characteristics of infants treated for hypoxic-ischaemic encephalopathy in England, Wales and Scotland: a population-based study using the National Neonatal Research Database
Authors: Hage Lory , Jeyakumaran Dusha , Dorling Jon , Ojha Shalini , Sharkey Don , Longford Nicholas , Modi Neena , Battersby Cheryl , Gale Chris
Published: February 2021

Background

Therapeutic hypothermia is standard of care for babies with moderate/severe hypoxic-ischaemic encephalopathy and is increasingly used for mild encephalopathy.

Objective

Describe temporal trends in the clinical condition of babies diagnosed with hypoxic-ischaemic encephalopathy who received therapeutic hypothermia.

Design

Retrospective cohort study using data held in the National Neonatal Research Database.

Setting

National Health Service neonatal units in England, Wales and Scotland.

Patients

Infants born from 1 January 2010 to 31 December 2017 with a recorded diagnosis of hypoxic-ischaemic encephalopathy who received therapeutic hypothermia for at least 3 days or died in this period.

Main outcomes

Primary outcomes: recorded clinical characteristics including umbilical cord pH; Apgar score; newborn resuscitation; seizures and treatment on day 1. Secondary outcomes: recorded hypoxic-ischaemic encephalopathy grade.

Results

5201 babies with a diagnosis of hypoxic-ischaemic encephalopathy received therapeutic hypothermia or died; annual numbers increased over the study period. A decreasing proportion had clinical characteristics of severe hypoxia ischaemia or a diagnosis of moderate or severe hypoxic-ischaemic encephalopathy, trends were statistically significant and consistent across multiple clinical characteristics used as markers of severity.

Conclusions

Treatment with therapeutic hypothermia for hypoxic-ischaemic encephalopathy has increased in England, Scotland and Wales. An increasing proportion of treated infants have a diagnosis of mild hypoxic-ischaemic encephalopathy or have less severe clinical markers of hypoxia. This highlights the importance of determining the role of hypothermia in mild hypoxic-ischaemic encephalopathy. Receipt of therapeutic hypothermia is unlikely to be a useful marker for assessing changes in the incidence of brain injury over time.
Patient education materials to implement choosing wisely recommendations for internal medicine at the emergency department
Authors: Laan Bart J , Huiszoon Willemijn B , Holleman Frits , Boermeester Marja A , Kaasjager Karin A H , Geerlings Suzanne E
Published: February 2021

Background

Choosing Wisely aims to reduce low-value care to improve quality and lower costs. In the Netherlands, this campaign offers three recommendations for internal medicine applicable in emergency departments (EDs): (1) do not place an indwelling urinary catheter in non-critically ill patients who can void; (2) do not order plain abdominal radiographs in patients with acute abdominal pain; and (3) discuss whether treatment limitations are needed. This quality improvement project aims to increase the implementation of the recommendations by patient information leaflets.

Methods

In a prospective before–after study, we collected data every other week during baseline and intervention periods (both 7 months) in two university medical centres. The primary outcomes were the adherence rates to the recommendations.

Results

805 patients visited the EDs for internal medicine, of whom 391 (48.6%) were hospitalised. Only 153 (19%) patients received the information leaflet. We found no change in implementation rates of the recommendations after the introduction of the patient information leaflet. In the baseline period, 28 patients received a urinary catheter, of whom 5 (17.9%) had no appropriate indication, compared with 4 (25.0%) of 16 patients in the intervention period (p=0.572). Unnecessary abdominal X-ray occurred once in the baseline period and not in the intervention period. Treatment limitations were not reported in 13 (6.5%) of 200 hospitalised patients in the baseline period, and in 17 (8.9%) of 191 patients in the intervention period (p=0.373).

Conclusions

Patient information leaflets did not increase the implementation of Choosing Wisely recommendations, which can be due to a high baseline rate and a poor dissemination of leaflets. Our ED seems not to be a practicable setting for dissemination of leaflets, since staff engagement was not possible due to high workload and shortage of qualified nursing staff in the Netherlands.
Improving antibiotic initiation and duration prescribing among nursing home physicians using an audit and feedback intervention: a theory-informed qualitative analysis
Authors: Laur Celia , Sribaskaran Thivja , Simeoni Michelle , Desveaux Laura , Daneman Nick , Mulhall Cara , Lam Jonathan , Ivers Noah Michael
Published: February 2021

Background

In nursing homes, 25%–75% of antibiotic days of treatment are inappropriate or unnecessary and are often continued for longer durations than necessary. In Ontario, physicians can receive a provincial audit and feedback report that provides individualised, confidential, data about their antibiotic prescribing. Objectives of this study were to explore antibiotic prescribing of nursing home physicians and the influence of the report.

Methods

All physicians who received a personalisedMyPractice: Long-Term Carereport from Ontario Health (Quality) (OH(Q)) in January 2019 (n=361) were eligible to participate in semistructured telephone interviews that were recorded then transcribed verbatim. Recruitment emails were sent from OH(Q) until saturation of ideas. Analysis was conducted by two team members inductively, then deductively using the theoretical domains framework, a comprehensive, theory-informed framework to classify determinants of specific behaviours.

Results

Interviews were conducted with n=18 physicians; 78% (n=14) were men, practising for an average of 27 years, with 18 years of experience working in nursing homes. Physicians worked in a median of 2 facilities (range 1–6), with 72% (n=13) in an urban setting. 56% (n=10) were medical directors for at least one home.Professional role and identityimpacted all aspects of antibiotic prescribing. Key roles included being an ‘Appropriate prescriber’, an ‘Educator’ and a ‘Change driver’. For antibiotic initiation, these roles interacted withKnowledge,Skills,Beliefs about consequence,Beliefs about capabilities,andSocial influenceto determine the resulting prescribing behaviour. When considering the impact of interacting with the report, participants’ perceived roles interacted withReinforcement,Social influence,andIntention. Environmental context and resourceswas an overarching domain.

Conclusion

This theory-informed approach is being used to inform upcoming versions of existing audit and feedback initiatives. Appealing to the role that prescribers see themselves offers a unique opportunity to encourage desired changes, such as providing tools for physicians to be Educators and facilitating, particularly medical directors, to be Change drivers.