bluuebunny/crossref_metadata_2025 huggingface dataset:
A Forced Response Analysis and Application of Impact Dampers to Rotordynamic Vibration Suppression in a Cryogenic Environment
Authors: Moore J. J. , Palazzolo A. , Gadangi R. , Nale T. A. , Klusman S. A. , Brown G. V. , Kascak A. F.
Published: March 2021

A high speed damper test rig has been assembled at Texas A&M University to develop rotordynamic dampers for rocket engine turbopumps that operate at cryogenic temperatures, such as those used in the Space Shuttle Main Engines (SSMEs). Damping is difficult to obtain in this class of turbomachinery due to the low temperature and viscosity of the operating fluid. An impact damper has been designed and tested as a means to obtain effective damping in a rotorbearing system. The performance and behavior of the impact damper is verified experimentally in a cryogenic test rig at Texas A&M. Analytical investigations indicate a strong amplitude dependence on the performance of the impact damper. An optimum operating amplitude exists and is determined both analytically and experimentally. In addition, the damper performance is characterized by an equivalent viscous damping coefficient. The test results prove the impact damper to be a viable means to suppress vibration in a cryogenic rotorbearing system.
A Variational Method for Solving Vibration Problems
Authors: Shirahatti Uday S. , Raju Pollapragada K.
Published: March 2021

Rayleigh-Ritz and Galerkin methods are frequently used in engineering to solve boundary value and eigenvalue problems. The success in applying these methods depends entirely on the construction of a variational entity called the functional, and the choice of a system of elements known as the basis functions. This in some cases greatly narrows down the class of problems to which the above methods may be applied. Here, we present a specific but sufficiently general method known as the Methods of Moments for constructing the elements going into the expansion of the approximate solution. The Method of Moments has been shown to posses the capability of generating the basis functions successfully. The Method of Moments in its various forms has been widely used in electromagnetism. Due to generality involved in the construction of these basis functions, the Method of Moments may be readily used to solve a large variety of problems arising in discrete as well as continuous vibrating systems. This idea forms the central theme of this article.
Vibration of Roller Chain Drives at Low, Medium and High Operating Speeds
Authors: Choi Woosuk , Johnson Glen E.
Published: March 2021

A model based on axially moving material is developed to study transverse vibration in roller chain drives. A unique feature of the work presented in this study is that impact, polygonal action and external periodic load have been included through chain tension and boundary conditions and periodic length change is also considered. The impact between the engaging roller and sprocket surface is modeled as a single impact between two elastic bodies and the modeling of the polygonal action is based on a four bar mechanism (rigid four bar at low speeds, elastic four bar at moderate and high speeds). At low and medium operating speeds, the system equation of motion for the chain span is expressed as a mixed type partial differential equation with time-dependent coefficients and time-dependent boundary conditions. At high operating speeds, the system equations of motion are two partial differential equations for transverse and longitudinal vibrations respectively and they are nonlinearly coupled The effects on transverse vibration of center distance, the moment of inertia of the driven sprocket system, static tension, and external periodic load are presented and discussed. Solutions are obtained by a finite difference method and Galerkin’s method.
An Experimental and Theoretical Study of Dynamic Structural Stiffness in Compliant Foil Bearings
Authors: Ku C.-P. Roger
Published: March 2021

This paper describes an experimental investigation into the dynamic characteristics of corrugated foil (bump foil) strips used in compliant surface foil bearings. This study provided the first opportunity to quantify the dynamic structural stiffness of bump foil strips for a wide range of operating conditions. The experimental data were compared to results obtained by a theoretical model developed earlier, and the comparisons show very good agreement. The effects of bearing design parameters, such as static loads, dynamic displacement amplitudes, bump configurations, pivot locations, surface coatings, and lubricant were also evaluated. An understanding of the dynamic characteristics of bump foil strips resulting from this work offers designers a means for enhancing the design of high-performance compliant foil bearings.
Passive Control of Vortex Shedding Induced Vibration of a Five-Hole Probe
Authors: Kimerer Neil B.
Published: March 2021

Vortex shedding in flow over a five-hole probe, used to measure three dimensional flow, excites the probe into vibration which causes measurement errors and acoustically induced structural fatigue of the probe stem. One method of reducing the coherent structure of the shed vortices and thereby reduce the vibration is to place a fin on the probe shaft with the fin free to rotate around the shaft. In a particular five-hole probe application there was no room for a fin so an alternate method of breaking up the coherent structure in the vortices was required. Coiling a wire around the probe was a technique tried using several wire diameters and coil spacings. Vibration levels were measured and analyzed for several wire coil configurations and compared to the vibration reduction achieved by the fin.
Method for Determining System Eigenvalues From FRF for Noise Contaminated Subsystems
Authors: Chen H. C. , Lee Eric K. , Tsuei Y. G.
Published: March 2021

A method for determining the eigenvalues of a synthesized system from the Frequency Response Function (FRF) for noise contaminated subsystems is presented. This method first uses matrix Auto-Regressive Moving-Average (ARMA) model in the Laplace domain to describe each subsystem. Then a modal force method by ARMA model can be established. Only the FRF at the connecting joints is needed in the analysis to form a matrix named Modal Force Matrix. From this matrix, both synthesized system modes and substructure modes can be extracted simultaneously. Since the inverse operation is not required to form Modal Force Matrix, the computation is reduced drastically. The eigensolution of the system in any frequency range can be determined independently. Numerical study suggests that good results can be achieved by this method.
Longitudinal Impact of a Rectilinear Elastic Link in Kinematics Chains
Authors: Marghitu Dan B. , Hurmuzlu Yildirim
Published: March 2021

In this article we consider the longitudinal impact of a rectilinear elastic link against a solid using Hertz contact theory. The main objective is to develop an analytical model that incorporates the effect of the general motion on the vibration of elastic elements in kinematic mechanisms. Equations for the translational and rotational motions of the link are developed by applying Hamilton’s principle. Kinetic energy that is required for the application of this principle has been derived by utilizing a generalized velocity field theory for elastic solids. This approach provides means to include the inertia terms directly in the equations of motion. Effects such as centrifugal stiffening and vibrations induced by Coriolis forces are accommodated automatically, rather than with the aid of ad hoc provisions. With the Dirac delta function defined as the limit of a sequence of functions we solve the discontinuities due to the impact.
Crack Detection in Composite Driving Shafts by Experimental Modal Analysis
Authors: Irretier H.
Published: March 2021

A case study is presented in which a composite driving shaft of a motor-bike was loaded with different increasing numbers of load-cycles in a pulsating testing machine to reach different stages of damage. For each number of load-cycles an experimental modal analysis was performed by an iterative, global, multi-degree-of-freedom, frequency-domain modal testing technique and the eigenfrequencies and modal damping ratios were identified. From the results it is shown that the damping increases with the number of load-cycles i.e. the state of damage. However, it turned out that a more sensitive indicator for the state of damage is the splitting and shifting of the ‘double’ eigenfrequencies of the bending modes of the driving shaft with the ‘axisymmetric’ circular ring cross section. This fact is shown on the basis of several related experimental data.
Singularity of Constraint Mechanical Systems
Authors: Wang J. Y. , Wu J. K.
Published: March 2021

The solution set of nonlinear kinematic constraint equations can be divided into regular and critical solution subsets, according to linear dependency of gradient vectors of the constraint equations. However, relative to a given input coordinate set, the solution set can also be separated into singular and nonsingular solution subsets, according to whether the sub-Jacobian matrix with respect to the output and intermediate coordinates is rank deficient or not. By providing precise definitions and classifications of singular configurations, from both mathematical and physical points of view, a better understanding of the kinematic behavior of singularity is obtained. Moreover, by extending the definition of the singular solution set to the output space and exploring the mathematical meaning of it, the difficulty in formulating mathematical expressions for workspace problems is resolved.
On the Derivation of Nonlinear and Linearized Models of Flexible Bodies in Large Global Motion
Authors: Lee Jung-Hwan , Uicker John J.
Published: March 2021

This paper presents a systematic modeling technique for systems of flexible bodies in large global motion. 4 × 4 homogeneous coordinate transformation matrices are used together with the Finite Element Method. By using homogeneous coordinates, derivatives of the transformation matrices can be represented by differential operator matrices. Due to this fact, one can derive the equations of motion in explicit matrix form. In this paper, the derivation of the general linearized as well as the nonlinear equations of motion are presented. Two typical mechanisms are chosen to show the validity of the procedures. Time history analysis and frequency domain analysis have been done using the mechanism models. The modal time integration technique has been applied to show the validity of the linearized equations of motion. The eigenvalues and eigenvectors of the mechanisms are used for the time integration of the linearized equations. For the frequency domain analysis, plots of changes in natural frequencies of the mechanisms are shown. These results show not only the dynamic properties of the structural parts of mechanism, but also those of the rigid body motions of the mechanism.
Application of Concurrent Engineering to Hi-Tech Product Realization
Authors: Pratt Michael K. , Deutsch Patricia B.
Published: March 2021

Since 1986, when the Institute for Defense Analysis first coined the term “concurrent engineering” (Carter and Baker, 1991), there has been much talked about and written on the subject. Early treatments of this subject focused principally on increasing the synergy between product development and manufacturing process development. Today’s increasing time-to-market pressures force the extension of the scope of this concurrent strategy to include all processes, such as customer training, documentation, and installation and field support, required to launch a new product successfully in a competitive industry.

Even with this larger scope, the competitive advantages of a concurrent strategy are well proven (Vesey, 1991) (Port et al, 1990) — there is no need for additional motivation. Hence, this paper addresses a specific strategy for implementing concurrent engineering in the real world. The context for this subject is the experiences on a large development project at DSC Communications Corporation, addressing the following: 1) the situation at the onset of the project, 2) what was done to implement concurrent engineering, and 3) the results of having committed to concurrent engineering. The final section offers some experience-based advice in terms of critical success factors.
Suspension Design Optimization of a Washing Machine: Part I — Modeling and Validation Results
Authors: Türkay O. S. , Tuğcu A. K. , Sümer I. T. , Kiray B.
Published: March 2021

The development of a non-linear time invariant rigid body dynamic model and the experimental validation of the suspension system of a horizontal-axis washing machine has been discussed in previous works by the authors. In this paper (Part I), modeling and experimental validation of a different suspension configuration of a test washing machine is assessed. The simulation model predicts the transient and steady-state vertical and horizontal amplitudes within maximum errors of 10% and 14%, respectively. The results are consistent with the results of the previous work. Thus, the simulation software code is verified for a generalized suspension design optimization of horizontal-axis washing machines.

In a companion paper (Part II), various formulations are discussed to select an objective function for parametric suspension design optimization and a parametric grid optimization method is implemented to the test washing machine introduced in this paper.
Application of an Information-Based Design for Assembly Theory to Assembly Workstation Design
Authors: Hunt David O. , Sturges Robert H.
Published: March 2021

An effective presentation of components at the workstation can have a significant impact in reducing assembly time. Our goal is to reduce the assembly time by optimization of the component presentation. The assembly factors recognized in Design for Assembly theory as relevant to both parts acquisition and assembly workstation layout are recognition, orientation, weight, and handling distance. This study considers a single manual assembler at an assembly station, with the components in rectangular bins of differing sizes and aspect ratios. Ninety degree rotations are allowed for minimizing potential handling distance. The assembly task is modelled with multiple assembly points representing the final location of the components. Components can be preoriented or random in the bins, with preorientation removing the recognition and orientation time penalties. The problem formulation employs Mixed Integer Non-Linear Programming (MINLP), and numerical evidence suggests an np-hard problem. Heuristic methods control computational time to practical levels for realistic assembly tasks. Our results show that numerical optimization of assembly workstation layout can reduce the expected level of difficulty over random or manual workstation design methods.
A Knowledge-Based Engineering System for the Design of Injection Molded Plastic Parts
Authors: Pratt S. D. , Sivakumar M. , Manoochehri S.
Published: March 2021

This study presents a knowledge-based engineering system for the design of injection molded plastic parts which is built around a commercial object-oriented design language. Knowledge-based engineering is an implementation paradigm in which the knowledge about the part is stored along with its geometry and the knowledge is used to verify the manufacturability and processability of the part. This system enables the designer to represent the plastic part in terms of hybrid features which associate product and process knowledge with part geometry. Engineering rules about part moldability and strength, process and material considerations, and mold design are captured in the system. To illustrate the capability and application of the system to real-world problems, the design of an enclosure for a portable data entry device is pursued. This exercise demonstrates the effectiveness and robustness of the system which applied appropriate rules at different stages of design to make the part inherently moldable.
Theoretical Analysis of Link Length Errors in Large Guided Chain Systems
Authors: Jin Y. , Carpino M.
Published: March 2021

Large guided chains are often used in manufacturing machinery to move materials and tooling. In such applications, the accuracy of the motion of the chain has a significant impact on the quality and yield of the process. The motion of the chain will be dependent on the geometry of the machine, the dynamic parameters of the machine, and the exact tolerances of the machine components. The research presented in this paper will first address the kinematics of a chain system. The analysis will include both chordal effects and link length variations, which affect the engagement between the chain and the drive sprocket. Second, the kinematic analysis will be used to develop a dynamic analysis based upon Lagrange’s equations for a chain system with variable link lengths. Results are presented which demonstrate the influence of chain mass and drive stiffness on the dynamic behavior of the system operating at both low and high speeds with oversized links.
Reliability-Based Optimal Design of a Bistable Compliant Mechanism
Authors: Howell L. L. , Rao S. S. , Midha A.
Published: March 2021

Compliant mechanisms obtain at least some of their motion from the deflection of their flexible members. Advantages of such mechanisms include the reduction of manufacturing and assembly cost and time. Bistable mechanisms are particularly useful in applications where two stable equilibrium positions are required, such as switches, gates, and closures. Fatigue is a major concern in many compliant mechanisms due to the cyclic stresses induced on the flexible members. In this paper, a method for the probabilistic design of a bistable compliant slider-crank mechanism is proposed. Link lengths, material properties, and cross-section dimensions are taken as random variables. Probabilistic constraints on the maximum and minimum required input torque, location of stable equilibrium position, and overall size are included. The objective function is the maximization of the mechanism reliability in fatigue. Several design studies are performed to gain further insight into the nature of the problem.
Component Selection Using Genetic Algorithms
Authors: Carlson Susan E. , Ingrim Michael , Shonkwiler Ronald
Published: March 2021

Genetic algorithms are investigated for use in obtaining optimal component configurations in dynamic engineering systems. Given a system layout, a database of component information from manufacturers’ catalogs, and a design specification, genetic algorithms are used to successfully select an optimal set of components. Five different algorithms are investigated for use on an hydraulic example. The algorithms are compared on the basis of expected hitting lime: the number of system simulations required to find the solution. One algorithm is found to have the best set of characteristics for solving component selection problems.
Design of Planar 3-R Robotic Workcells in Two-Space With Rotation at the Third Joint Limited to Exactly One Turn
Authors: Soman N. A. , Davidson Joseph K.
Published: March 2021

An interactive graphics-based computer scheme was developed that determines suitable locations for a workpiece, and its associated task-motion, in the dexterous workspace of a three-hinged planar robotic workcell. It determines all acceptable positions for the first joint of the robot relative to the workpiece; therefore, all solutions are represented as an area in two dimensions, unlike existing methods of motion-planning that present them as a volume in a three-dimensional joint-space for the same planar robot. This simplifies the solution-space by reducing its dimension from three to two. The method differentiates between the constraints that singular configurations, workspace boundaries, the excursion-range of one full turn at the third rotary joint, and physical obstacles impose on the design of a planar robotic workcell, thus giving a better understanding of the global properties and physical limitations of the workcell. All possible acceptable designs appear in a graphical form that can be readily visualized and be directly measured in a Cartesian frame of reference in the workcell. The method can be applied to either open or closed motion trajectories. Applications include the design of robotic workcells that are used for fusion welding and for deposition of adhesives, where, in each case, the attitude of the end-effector is as important to the task as is the path that a point on the tool follows.
Data Localization Algorithms for Automated Inspection
Authors: Choi Woncheol , Kurfess Thomas R.
Published: March 2021

For automated inspection, correlating measured data with original design geometry and tolerance specification is of fundamental necessity. In order to compare measured data to nominal geometry, it is necessary to find an exact location of the measured points with respect to a nominal geometry coordinate system. If a tolerance zone is provided, its boundaries must be compared to the measured points to determine the quality and functionality of the part. The problem of localizing measured data can be formalized as an unconstrained optimization problems. In this paper, we develop the localization algorithms using the least square criterion. Such a localization algorithm can also place the measured data into tolerance zone, when it is specified.
Notes on Interpreting Monotonicity Analysis Using Karush-Kuhn-Tucker Conditions and MONO: A Logic Program for Monotonicity Analysis
Authors: Hsu Yeh-Liang
Published: March 2021

The Monotonicity Principles are only necessary conditions. All principles are under the condition “if the problem is well constrained”. But one of the important purposes of Monotonicity Analysis is to identify optimization models that are not well constrained. Before applying Monotonicity Principles to a problem, whether the problem is well constrained is not known. This paper attempts to clarify some potential problems of Monotonicity Analysis when applying to not-well-constrained problems. These problems can be easily explained using the Karush-Kuhn-Tucker optimality conditions. Ways to prevent the users from reaching erroneous results in these situations are proposed. These results are implemented in the computer program MONO. MONO is a logic program which automatically generates rigorous Monotonicity Analysis steps and global facts about the optimization model. Hardware and software requirements of this program are minimal. A hydraulic cylinder design example is used to demonstrate the program.
Hybrid Feature Extraction for Machining Applications
Authors: Fields Malcolm C. , Anderson D. C.
Published: March 2021

A hybrid feature extraction algorithm for extracting cavity features for machining applications is presented. The algorithm operates on both a feature-based solid model of a part and its corresponding boundary representation solid model. Information available from both part representations is used, offering a more robust and efficient solution for some of the critical limitations of current feature extraction algorithms, such as verification of completeness, computation of cavity volumes, and maintenance of design information.

The hybrid feature extraction algorithm combines the strengths of feature-based design and feature extraction approaches to linking design and manufacturing. Starting with a feature-based model of a part consisting of volumetric design features combined with a stock shape using set operations, the algorithm transforms this model into a feature model containing only machinable cavity features. The transformation involves computations on both the set theoretic feature model and its corresponding boundary representation solid model, and deals with the complexities of feature-feature intersections and protrusions. By combining the higher-level product information contained in the design feature model with the topological and geometric information in the boundary representation model, the algorithm supplements traditional boundary representation extraction with non-geometric product information, enabling the verification of completeness, and significantly aiding the computation of the appropriate feature volumes.
Computing Equidistant Curves and Surfaces
Authors: Sarma R. , Dutta D.
Published: March 2021

The problem of computing equidistant curves and surfaces between a point and (i) a parametric curve and (ii) a parametric surface is considered. This problem is important since it can form a basis for further generalizations of the problem, viz., computing equidistant curves and surfaces between a pair of curves and a pair of surfaces. Engineering applications of such equidistant curves and surfaces include fluid flow analysis, mesh generation and shape interrogation.
Representation of Relative Freedom Derived From Geometric Models
Authors: Laowattana Schitt , Sturges Robert H.
Published: March 2021

Multi-contact constraints representing the assembled state of polygonal solid objects can be represented by screw systems which provide a complete description of rotational and translational freedom. In most cases, the computation of relative freedom does not require consideration of all constraints. We have developed an algorithm to identify redundant constraints, therefore minimizing the complexity of assembly/disassembly planning. We also employ the method to determine relative stability which identifies unstable configurations of assembled parts.
Economic Analysis of Quality Innovation in Design and Manufacturing
Authors: Vasseur Hubert , Kurfess Thomas R. , Cagan Jonathan
Published: March 2021

Due to several possible production modes, an industrial output may have different quality levels. Production processes and quality assurance plans are chosen and adjusted, generally as a lagged reaction to customers’ input and competitors’ strategy. Different techniques based on cost benefit analysis have existed to assess beforehand the overall benefits to society of such decisions; however, these techniques do not necessarily provide any insight as to the resulting influence on corporate profits. This paper reviews different perspectives on industrial quality and adopts a formalism in which social and corporate optimum can be compared from an engineering standpoint. The potential benefits for a manufacturer to improve the quality of its products are studied under several market conditions. The incentive is the strongest in a competitive environment where the benefits of quality innovation are twofold: quality innovation increases consumers’ demand and allows the manufacturer to keep more substantial profit margins.
Optimal Heat Sink Design and Component Placement Using the Ellipsoid Method
Authors: Urban Carl T. , Gabriele Gary A.
Published: March 2021

In the electronic products market, intense competition from overseas has made product cost, performance and time-to-market critical factors to a company’s survival. While recent advances in manufacturing methods and material handling systems have aided in this struggle, the decisions made in the early stages of design still control an overwhelming majority of a product’s final cost and delivery schedule. These decisions affect the entire life-cycle of the product from design, through the customer’s use, to disposal.

This paper describes the development of a simple heat sink component placement optimization procedure using the Ellipsoid Algorithm. Two heat sink geometries were modelled to determine their steady state temperature distributions and the component junction temperature(s). By relocating the component(s), the Ellipsoid Algorithm sought to minimize the heat sink assembly’s failure rate. The effect of heat sink size on assembly reliability is also presented. The heat sink thermal model was formulated using finite differences and written in Fortran 77.
Modeling Evolving Product Data for Concurrent Engineering
Authors: Cleetus K. J.
Published: March 2021

In order to make the traditional product structure tree representation amenable to concurrent engineering, relationships like perspective-of and dependent-on have to be added to the essential part-of relationship. Complex data can be held in proprietary formats, while simple data will be in a common representation for direct access by diverse disciplines. Coordination among team members in a project can be carried out using such a model. Besides, a virtually unified view of all the data is possible, though they may lie in distributed and heterogeneous data bases. A very necessary characteristic of such a model is that its time evolution should be easy to represent in order to reflect the dynamic nature of product development, where the model itself, and not merely the data values change. Managing versions is also facilitated by the comprehensive structure of the Unified Product Data Model (UPDM).
Enhancement in the tribological performance of WSx/a-C multilayer films with Al sublayers in vacuum
Authors: Yang Fang-er , Zhang Wan-kun , Wang Gong-qi , Wang Tao , Zheng Xiao-hua
Published: March 2021

The manufacturing of multilayer films with improved mechanical and tribological properties has attracted attention recently for enabling their space applications. In this study, we aim to optimize the manufacturing process of WSx/a-C multilayer films by alternately depositing WS2, amorphous carbon (a-C), and Al metal on silicon substrates through magnetron sputtering. The microstructure and morphology of the multilayer films were investigated by x-ray diffractometry, scanning electron microscopy, and x-ray photoelectron spectroscopy. The mechanical and tribological properties of the films were evaluated in vacuum using a nanoindentation tester, ball-on-disk tribometer, and scratch tester. The results showed that the addition of an Al layer with an optimal thickness refined the microstructure of the films. The tribological properties of the films deteriorated with increasing thickness of the Al single layer. When the thickness of the Al film was 1 nm, the tribological properties of the films were optimal, and the adhesion was maximum (49.1 N). Hardness of the films gradually decreased with an increase in the thickness. Wear rate of the films decreased initially and then increased, and the wear rate was lowest when the thickness of the Al single layer was 2 nm (1.41 × 10−15 m3 N−1 m−1). By manufacturing films with optimal thickness, suitable tribological properties for vacuum applications can be achieved.
Physical Education Teachers’ Experiences With Remote Instruction During the Initial Phase of the COVID-19 Pandemic
Authors: Mercier Kevin , Centeio Erin , Garn Alex , Erwin Heather , Marttinen Risto , Foley John
Published: March 2021

This study investigated physical education (PE) teachers’ experiences with remote instruction in the United States during the initial outbreak of COVID-19. PE teachers (n = 4,362) from all 50 states completed a survey identifying their experiences with remote instruction in May, 2020. Survey responses were analyzed by geographic region, district type, and school level. Teachers reported having students submit assignments (51% yes), using video instruction (37% yes), being less effective when instructing remotely (20% yes), and emphasizing student outcomes focused on health-related fitness (32% yes), and physical activity value/enjoyment (43% yes). Access to technology (40% yes) and required student assignments (43% yes) were lowest among teachers from the South. Rural teachers reported the least access to technology (37% yes) and rated themselves as least effective (24% yes). Secondary level teachers reported the highest percentage of required assignments (84% yes). Teachers’ responses identify unique challenges to delivering equitable and effective remote PE instruction.
Manta-like planktivorous sharks in Late Cretaceous oceans
Authors: Vullo Romain , Frey Eberhard , Ifrim Christina , González González Margarito A. , Stinnesbeck Eva S. , Stinnesbeck Wolfgang
Published: March 2021

A soaring shark

Modern sharks occupy marine ecosystems across the world but display little morphological diversity, being mostly streamlined predators. Vullo
et al.
describe a new species of shark from the late Cretaceous that shows that the lack of current variation is not due to limited morphological “exploration” in the past. Specifically,
Aquilolamna milarcae
displays many features similar to modern manta rays, notably long, slender fins and a mouth seemingly adapted to filter feeding, suggesting that it was planktivorous. This finding indicates both that elasmobranchs evolutionarily experimented with other forms and that the planktivorous “soarers” emerged in this group at least 30 million years earlier than previously recognized.

Science
, this issue p.
1253
Processive RNA polymerization and promoter recognition in an RNA World
Authors: Cojocaru Razvan , Unrau Peter J.
Published: March 2021

A processive RNA replicator

The RNA World Hypothesis suggests that, before modern life, there were RNA molecules that were capable of carrying genetic information and driving chemical reactions, a task gradually replaced by DNA and enzymes in modern biology. Central to this theory is an RNA replicase capable of mediating general replication of RNA. Using laboratory evolution, Cojocaru
et al.
isolated a promoter-based RNA polymerase ribozyme that, analogous to modern-day protein polymerases, clamps onto templates to increase its processivity, making it a potential model for replication in early biology.

Science
, this issue p.
1225
Using satellite imagery to understand and promote sustainable development
Authors: Burke Marshall , Driscoll Anne , Lobell David B. , Ermon Stefano
Published: March 2021

Satellite monitoring of development

Recent years have witnessed rapid growth in satellite-based approaches to quantifying aspects of land use, especially those monitoring the outcomes of sustainable development programs. Burke
et al.
reviewed this recent progress with a particular focus on machine-learning approaches and artificial intelligence methods. Drawing on examples mostly from Africa, they conclude that satellite-based methods enhance rather than replace ground-based data collection, and progress depends on a combined approach.

Science
, this issue p.
eabe8628
Justice, diversity, and research ethics review
Authors: Strauss David H. , White Sarah A. , Bierer Barbara E.
Published: March 2021

It is time for institutional review boards and research ethics committees to address the ethics of inclusion
Generating arbitrary topological windings of a non-Hermitian band
Authors: Wang Kai , Dutt Avik , Yang Ki Youl , Wojcik Casey C. , Vučković Jelena , Fan Shanhui
Published: March 2021

Topology in the open

Controlling the topology of a system provides a route to develop devices that are robust against defects. Whereas earlier developments of topological band theory focused on Hermitian (closed) systems, recent efforts have been toward non-Hermitian (open) systems. K. Wang
et al.
report on the measurement and control of topologically nontrivial windings of a non-Hermitian energy band. By implementing non-Hermitian lattice Hamiltonians along a frequency synthetic dimension formed by optical frequency modes in a modulated ring-resonator, they directly visualized the nontrivial topological band winding and showed that the winding can be controlled. Such control provides a route for the experimental synthesis, characterization, and control of topologically nontrivial phases in open physical systems.

Science
, this issue p.
1240
A Phase I Evaluation of the Pharmacokinetics and Tolerability of the HIV-1 Maturation Inhibitor GSK3640254 and Tenofovir Alafenamide/Emtricitabine in Healthy Participants
Authors: Pene Dumitrescu Teodora , Joshi Samit R. , Xu Jianfeng , Zhan Joyce , Johnson Mark , Butcher Laurie , Zimmerman Eric , Webster Lindsey , Davidson Antonia M. , Lataillade Max , Min Sherene
Published: March 2021

GSK3640254 is a next-generation maturation inhibitor that would likely be combined with standard antiretroviral agents to form a regimen of ≥2 fully active classes. This phase I, open-label, 2-period, 1-way study assessed potential pharmacokinetic (PK) interactions between GSK3640254 and tenofovir alafenamide/emtricitabine (TAF/FTC; including the metabolite tenofovir [TFV]) in healthy volunteers.
Responsiveness of Aromatoleum aromaticum EbN1
T
to Lignin-Derived Phenylpropanoids
Authors: Vagts Jannes , Kalvelage Kristin , Weiten Arne , Buschen Ramona , Gutsch Julian , Scheve Sabine , Wöhlbrand Lars , Diener Stefan , Wilkes Heinz , Winklhofer Michael , Rabus Ralf
Published: March 2021

Lignin is a ubiquitous heterobiopolymer built from a suite of 3-phenylpropanoid subunits. It accounts for more than 30% of the global plant dry material, and lignin-related compounds are increasingly released into the environment from anthropogenic sources, i.e., by wastewater effluents from the paper and pulp industry.
Nonessential Ribosomal Proteins in Bacteria and Archaea Identified Using Clusters of Orthologous Genes
Authors: Galperin Michael Y. , Wolf Yuri I. , Garushyants Sofya K. , Vera Alvarez Roberto , Koonin Eugene V.
Published: March 2021

In many prokaryote genomes, one or more ribosomal protein (RP) genes are missing. Analysis of 1,309 prokaryote genomes included in the Clusters of Orthologous Genes (COG) database shows that only about half of the RPs are universally conserved in bacteria and archaea.
Link between Interleukin-23 and Anti-CD4 Autoantibody Production in Antiretroviral-Treated HIV-Infected Individuals
Authors: Luo Zhenwu , Li Min , Mi Fuli , Meng Zhefeng , Du Guoqiang , Martin Lisa , Liu Hui , Jin Ping , Stroncek David , Heath Sonya L. , Jiang Wei
Published: March 2021

In our published studies, we determined that pathological anti-CD4 IgGs from immunologic nonresponders on virally suppressive ART (CD4 cell counts < 350 cells/μl) mediated CD4
+
T cell death via antibody-mediated cytotoxicity (ADCC), which plays a role in poor CD4
+
T cell recovery from ART. Up to 25% of HIV-infected individuals are nonresponders and demonstrate increased morbidity and mortality.
Two key switches in regional stress field during multi-stage deformation in the Carboniferous–Triassic southernmost Altaids (Beishan, NW China): Response to orocline-related roll-back processes
Authors: Tian Zhonghua , Xiao Wenjiao , Windley Brian F. , Huang Peng , Zhang Ji’en , Ao Songjian , Zhang Zhiyong , Song Dongfang , Liu Fulai
Published: March 2021

The orogenic architecture of the Altaids of Central Asia was created by multiple large-scale slab roll-back and oroclinal bending. However, no regional structural deformation related to roll-back processes has been described. In this paper, we report a structural study of the Beishan orogenic collage in the southernmost Altaids, which is located in the southern wing of the Tuva-Mongol Orocline. Our new field mapping and structural analysis integrated with an electron backscatter diffraction study, paleontology, U-Pb dating, 39Ar-40Ar dating, together with published isotopic ages enables us to construct a detailed deformation-time sequence: During D1 times many thrusts were propagated northwards. In D2 there was ductile sinistral shearing at 336–326 Ma. In D3 times there was top-to-W/WNW ductile thrusting at 303–289 Ma. Two phases of folding were defined as D4 and D5. Three stages of extensional events (E1–E3) separately occurred during D1–D5. Two switches of the regional stress field were identified in the Carboniferous to Early Permian (D1-E1-D2-D3-E2) and Late Permian to Early Triassic (D4-E3-D5). These two switches in the stress field were associated with formation of bimodal volcanic rocks, and an extensional interarc basin with deposition of Permian-Triassic sediments, which can be related to two stages of roll-back of the subduction zone on the Paleo-Asian oceanic margin. We demonstrate for the first time that two key stress field switches were responses to the formation of the Tuva-Mongol Orocline.
Supplemental Material: A newly discovered Late Cretaceous metamorphic belt along the active continental margin of the Neo-Tethys ocean
Authors: Wang Dan , al. et
Published: March 2021

Tables S1–S8, Figures S1–S8, and analytical methods.
Supplemental Material: Ancestral trans–North American Bell River system recorded in late Oligocene to early Miocene sediments in the Labrador Sea and Canadian Great Plains
Authors: Corradino Julia I. , Pullen Alex
Published: March 2021

S1: U-Pb data from the Saglek Basin Rut H-11 well and Canadian Great Plains samples; S2: Sr and Nd isotope data for marine bivalves in Saglek Basin Rut H-11 well.
Prevalence of glaucoma in the Lao People’s Democratic Republic: the Vientiane Eye Study
Authors: Guo Brad , Tan Yiran , Nygaard Stephen , Carrillo Cesar , Nouansavanh Kham Od , Souksamone Kitar , Casson Robert J
Published: March 2021

Aims

To determine the prevalence and subtypes of glaucoma in Vientiane Province.

Methods

We conducted a population-based study of 1264 participants aged ≥40 years of age from urban and rural areas of Vientiane Province. Data collection included Snellen visual acuity, slip lamp examination, tonometry, gonioscopy, dilated stereoscopic disc examination and perimetry. Glaucoma was categorised by clinical subtype.

Results

The mean age of the 1264 participants was 57.6 years; 91.9% of eyes had a gradable disc. The prevalence of glaucoma of any category in at least one eye was 1.54% (95% CI 0.66% to 3.59%). The overall prevalence of primary open-angle glaucoma, primary angle-closure glaucoma and secondary glaucoma was 0.62% (95% CI 0.19% to 1.98%), 0.55% (95% CI 0.12% to 2.54%) and 0.37% (95% CI 0.07% to 1.86%); 12 (66.7%) of participants with glaucoma were at least unilaterally blinded by WHO definition.

Conclusions

The prevalence of glaucoma in the Vientiane Eye Study is relatively low compared with the prevalence reported in other studies from Asian regions; however, the median age in this study was low, reflecting the age group of the population and the rapid urbanisation occurring in the Lao People’s Democratic Republic. Nevertheless, glaucoma remains a blinding disease in this population.
Predicting the safety zone for steroid-induced ocular hypertension induced by intravitreal dexamethasone implantation
Authors: Choi Wungrak , Bae Hyoung Won , Shin Hye Jung , Kim Eun Woo , Kim Chan Yun , Kim Min , Seong Gong Je
Published: March 2021

Background/aims

This study aimed to predict the possibility of steroid-induced ocular hypertension (OHT) after intravitreal dexamethasone (DEX) implantation and to identify a proper safety zone for such injections.

Methods

A cross-sectional observational study was conducted and included 908 patient eyes that underwent DEX implant injection due to various retinal diseases. Intraocular pressure (IOP) was measured before injection, at 1 week, and at 1, 2, 3, 6 and 12 months thereafter. Eyes of enrolled patients were divided into the OHT and normal IOP groups. Univariable logistic regression analysis was used to assess significant associations between steroid-induced OHT and covariates; significant and previously reported significant variables were analysed with a multivariable model, and predictive nomograms were developed.

Results

Age, sex, axial length, glaucomatous eye, neovascular glaucoma, secondary glaucoma, uveitis history, hypertension, depression, diabetes mellitus and a history of previous laser-assisted in-situ keratomileusis or laser-assisted subepithelial keratectomy were significantly related to steroid-induced OHT (p<0.05). The calibration plot revealed good prediction under a predicted value of 0.4. Cut-off values for 80%, 86%, 91%, 95% and 98% sensitivity and specificity were offered for the safety zone after intravitreal DEX implantation.

Conclusion

We developed two nomograms to predict a safety zone for intravitreal DEX implantation. These can be used to identify individuals who may be safely prescribed steroid treatments and for whom extra caution should be exercised.
ACL reconstruction for all is not cost-effective after acute ACL rupture
Authors: Eggerding Vincent , Reijman Max , Meuffels Duncan Edward , van Es Eline , van Arkel Ewoud , van den Brand Igor , van Linge Joost , Zijl Jacco , Bierma-Zeinstra Sita MA , Koopmanschap Marc
Published: March 2021

Objectives

To conduct a cost-utility analysis for two commonly used treatment strategies for patients after ACL rupture; early ACL reconstruction (index) versus rehabilitation plus an optional reconstruction in case of persistent instability (comparator).

Methods

Patients aged between 18 and 65 years of age with a recent ACL rupture (<2 months) were randomised between either an early ACL reconstruction (index) or a rehabilitation plus an optional reconstruction in case of persistent instability (comparator) after 3 months of rehabilitation. A cost-utility analysis was performed to compare both treatments over a 2-year follow-up. Cost-effectiveness was calculated as incremental costs per quality-adjusted life year (QALY) gained, using two perspectives: the healthcare system perspective and societal perspective. The uncertainty for costs and health effects was assessed by means of non-parametric bootstrapping.

Results

A total of 167 patients were included in the study, of which 85 were randomised to the early ACL reconstruction (index) group and 82 to the rehabilitation and optional reconstruction group (comparator). From the healthcare perspective it takes 48 460 € and from a societal perspective 78 179 €, to gain a QALY when performing early surgery compared with rehabilitation plus an optional reconstruction. This is unlikely to be cost-effective.

Conclusion

Routine early ACL reconstruction (index) is not considered cost-effective as compared with rehabilitation plus optional reconstruction for a standard ACL population (comparator) given the maximum willingness to pay of 20 000 €/QALY. Early recognition of the patients that have better outcome of early ACL reconstruction might make rehabilitation and optional reconstruction even more cost-effective.