bluuebunny/crossref_metadata_2025 huggingface dataset:
Unlocking the phylogenetic diversity, primary habitats, and abundances of free‐living Symbiodiniaceae on a coral reef
Authors: Fujise Lisa , Suggett David J. , Stat Michael , Kahlke Tim , Bunce Michael , Gardner Stephanie G. , Goyen Samantha , Woodcock Stephen , Ralph Peter J. , Seymour Justin R. , Siboni Nachshon , Nitschke Matthew R.
Published: November 2020

Dinoflagellates of the family Symbiodiniaceae form mutualistic symbioses with marine invertebrates such as reef‐building corals, but also inhabit reef environments as free‐living cells. Most coral species acquire Symbiodiniaceae horizontally from the surrounding environment during the larval and/or recruitment phase, however the phylogenetic diversity and ecology of free‐living Symbiodiniaceae on coral reefs is largely unknown. We coupled environmental DNA sequencing and genus‐specific qPCR to resolve the community structure and cell abundances of free‐living Symbiodiniaceae in the water column, sediment, and macroalgae and compared these to coral symbionts. Sampling was conducted at two time points, one of which coincided with the annual coral spawning event when recombination between hosts and free‐living Symbiodiniaceae is assumed to be critical. Amplicons of the internal transcribed spacer (ITS2) region were assigned to 12 of the 15 Symbiodiniaceae genera or genera‐equivalent lineages. Community compositions were separated by habitat, with water samples containing a high proportion of sequences corresponding to coral symbionts of the genus Cladocopium, potentially as a result of cell expulsion from in hospite populations. Sediment‐associated Symbiodiniaceae communities were distinct, potentially due to the presence of exclusively free‐living species. Intriguingly, macroalgal surfaces displayed the highest cell abundances of Symbiodiniaceae, suggesting a key role for macroalgae in ensuring the ecological success of corals through maintenance of a continuum between environmental and symbiotic populations of Symbiodiniaceae.
Structural and biochemical characterizations of the novel autolysin Acd24020 from Clostridioides difficile and its full‐function catalytic domain as a lytic enzyme
Authors: Sekiya Hiroshi , Tamai Eiji , Kawasaki Jurina , Murakami Kaho , Kamitori Shigehiro
Published: November 2020

Autolysin is a lytic enzyme that hydrolyzes peptidoglycans of the bacterial cell wall, with a catalytic domain and cell wall‐binding (CWB) domains, to be involved in different physiological functions that require bacterial cell wall remodeling. We identified a novel autolysin, Acd24020, from Clostridioides (Clostridium) difficile (C. difficile), with an endopeptidase catalytic domain belonging to the NlpC/P60 family and three bacterial Src‐homology 3 domains as CWB domains. The catalytic domain of Acd24020 (Acd24020‐CD) exhibited C. difficile‐specific lytic activity equivalent to Acd24020, indicating that Acd24020‐CD has full‐function as a lytic enzyme by itself. To elucidate the specific peptidoglycan‐recognition and catalytic reaction mechanisms of Acd24020‐CD, biochemical characterization, X‐ray structure determination, a modeling study of the enzyme/substrate complex, and mutagenesis analysis were performed. Acd24020‐CD has an hourglass‐shaped substrate‐binding groove across the molecule, which is responsible for recognizing the direct 3–4 cross‐linking structure unique to C. difficile peptidoglycan. Based on the X‐ray structure and modeling study, we propose a dynamic Cys/His catalyzing mechanism, in which the catalytic Cys299 and His354 residues dynamically change their conformations to complement each step of the enzyme catalytic reaction.
A safer, faster, leaner workplace? Technical‐maintenance worker perspectives on digital drone technology ‘effects’ in the European steel industry
Authors: Stroud Dean , Weinel Martin
Published: November 2020

This paper focuses on technical‐maintenance worker perspectives on the insertion of digitised drone technologies in the European steel industry. The industry is aiming for a ‘business model transformation’ by means of digitalisation, which includes the use of drone technologies for maintenance functions. In this paper, we explore on what basis might such workers embrace or resist this new technology. Drawing on data from a project investigating the use of drones for a ‘safer, faster and leaner’ workplace, we employ an analysis of technology ‘effects’ to discuss the risks and benefits to workers of drone technologies (see Orlikowski, Organ. Sci., 3, 1992, 398; Edwards and Ramirez, New Technol. Work Employ., 31, 2016, 99). The insertion and use of drone technology within the industry raises questions for the industry’s highly skilled workers and their representatives on the ‘effect’ of drone innovations on the industry’s existing structures and patterns of work.
Dynamic Inventory Allocation with Demand Learning for Seasonal Goods
Authors: Nambiar Mila , Simchi‐Levi David , Wang He
Published: November 2020

We study a multi‐period inventory allocation problem in a one‐warehouse multiple‐retailer setting with lost sales. At the start of a finite selling season, a fixed amount of inventory is available at the warehouse. Inventory can be allocated to the retailers over the course of the selling horizon (transshipment is not allowed). The objective is to minimize the total expected lost sales and holding costs. In each period, the decision maker can use the realized and possibly censored demand observations to dynamically update demand forecast and consequently make allocation decisions. Our model allows a general demand updating framework, which includes ARMA models or Bayesian methods as special cases. We propose a computationally tractable algorithm to solve the inventory allocation problem under demand learning using a Lagrangian relaxation technique, and show that the algorithm is asymptotically optimal. We further use this technique to investigate how demand learning would affect inventory allocation decisions in a two‐period setting. Using a combination of theoretical and numerical analysis, we show that demand learning provides an incentive for the decision maker to withhold inventory at the warehouse rather than allocating it in early periods.
Exploiting microalgal competition ability to acquire nitrogen and light
Authors: Liu Junying , Xia Donghua , Qiu Wen
Published: November 2020

Microalgae are ideal phototrophs for many commercial products. Our previous research has leveraged biodiversity concepts to evaluate the effects of competition on dynamics and coexistence of different microalgal species. The originality of the review lies in the envisioning of these state‐of‐the‐art techniques to study a novel issue of how algal species modulate the whole‐cell metabolism and gene expression to yield biomass beyond current limits. Competition is crucial in driving the activity, structure and composition of algal communities which are of central importance to aquatic environment productivity. However, fundamental gaps remain in understanding how algal species compete for light and nitrogen by regulating whole‐cell metabolisms. Moreover, it is unclear how this competitive potential is modulated in algal populations to achieve high biomass production. Despite the principles and applications of competition having been tested theoretically and empirically in many studies, there is still considerable debate and paradoxical observations regarding the key mechanisms that underlie competition for limited nutrients. One reason for the uncertainty is the difficulty in making direct comparisons between species with differing functional traits. Moreover, the lack of available reference genomes for many algal species presents a further hindrance in understanding competitive trait dynamics. The review seeks to improve our understanding of these fundamental problems, which have direct implications in aiding the production of renewable fuels and chemicals via photosynthetic biology. The review also envisions a whole set of omics analysis in the future that would shed light on the poorly defined functions of competition in microalgae.
Challenges in Isolating the Effect of College Attainment and Debt Accumulation on Young Adult Self‐Concept
Authors: Dirlam Jonathan , Merry Joseph
Published: November 2020

Prior studies have found college attendance to boost self‐esteem and mastery in young adults. Yet, college attendance itself is likely influenced by self‐esteem and mastery levels experienced in adolescence. And both are likely influenced by adolescent cognitive ability and academic achievement. Using data from the NLSY79‐YA, we illustrate the difficulties in isolating the positive effect of college on young adult self‐concept. First, we estimate adolescent self‐concept trajectories for respondents and analyze whether these trajectories are predictive of college attendance and degree attainment. Second, we assess whether the inclusion of adolescent self‐concept trajectories significantly reduces the beneficial effect of college on young adult self‐esteem and mastery. We also investigate the complex temporal relationship between adolescent characteristics, debt accumulation, and young adult self‐concept. Our findings show that the positive effects of college attainment and debt accumulation on young adult self‐concept are significantly reduced when measures of adolescent self‐concept and cognitive ability are included. These results imply that the benefit of going to college or acquiring debt may be overstated when adolescent characteristics are not taken into consideration.
Accuracy of clinical diagnosis and videodermoscopy in female pattern hair loss
Authors: Mancilla Gener‐Alejandro , Restrepo Rodrigo , Sanclemente Gloria
Published: November 2020

Background

Female pattern hair loss (FPHL) is a non‐scarring hair disease characterized by progressive hair diminishment and decrease of its density. Although typical cases of FPHL are usually straightforward to diagnose, its initial forms can be unrecognized and often need the use of other diagnostic methods.

Objective

To describe the accuracy of a diagnosis of FPHL based on clinical grounds and videodermoscopy compared with scalp biopsy.

Methods

An observational diagnostic test study was performed. Scalp biopsies were read by the same dermatopathologist and processed horizontally to allow follicle's number and size evaluation. Digital videodermoscopy was also performed.

Results

A total of 202 patients were enrolled, but only 35 women were assessed with digital videodermoscopy. When clinical diagnosis was compared to scalp biopsy, a sensitivity, specificity, positive predictive value (PPV), and a negative predictive value (NPV), of 77% %, 72.4%, 82.2%; and 65.5%, were respectively obtained. Videodermoscopy showed a sensitivity, specificity, PPV and NPV of 88.9%, 100%, 100%, and 72.7%, respectively.

Conclusions

This study provided valuable information on the accuracy of clinical examination of FPHL, showed the usefulness of videodermoscopy as a method that in the future may replace scalp biopsy for its diagnosis, or also could aid patient´s follow‐up.
Adjuvant doxorubicin vs metronomic cyclophosphamide and meloxicam vs surgery alone for cats with mammary carcinomas: A retrospective study of 137 cases
Authors: Petrucci Gonçalo N. , Henriques Joaquim , Lobo Luís , Vilhena Hugo , Figueira Ana C. , Canadas‐Sousa Ana , Dias‐Pereira Patrícia , Prada Justina , Pires Isabel , Queiroga Felisbina L.
Published: November 2020

This study aims to evaluate the efficacy and side effects of low dose cyclophosphamide chemotherapy plus meloxicam as an adjuvant treatment, compared with high dose doxorubicin or surgery alone in cats with mammary carcinoma. Medical records of 228 female cats treated for mammary carcinoma between 2008 and 2018, were reviewed in eight veterinary institutions. Only cats with complete tumour staging and radical mastectomy were included in the study. One hundred and thirty‐seven cats were divided into three treatment groups: group 1 (n = 80) cats treated with surgery, group 2 (n = 34) cats that had surgery and adjuvant treatment with doxorubicin, and group 3 (n = 23) cats with surgery and adjuvant treatment with low dose metronomic cyclophosphamide and meloxicam. The study endpoints were disease free interval (DFI) and overall survival (OS). Toxicity was evaluated according to the VCOG‐CTCAE criteria. The median DFI was 270, 226 and 372 days in groups 1, 2 and 3, respectively. The median OS was 338 (group 1), 421 (group 2) and 430 (group 3) days. The differences between groups were not significant (DFI P = .280 and OS P = .186). Toxicity was observed in 52.9% (n = 18) of cats in group 2 and 39.1% (n = 9) of cats in group 3, with mild to moderate intensity. Differences were not significant (P = .306). In conclusion, adjuvant chemotherapy treatment did not improve survival and the overall benefit remains unproven. Randomized prospective trials are necessary to clarify the effectiveness of adjuvant chemotherapy treatment for feline mammary carcinomas.
Endurance exercise plus overload induces fatigue resistance and similar hypertrophy in mice irrespective of muscle mass
Authors: Hendrickse Paul W. , Krusnauskas Raulas , Hodson‐Tole Emma , Venckunas Tomas , Degens Hans
Published: November 2020

New Findings

What is the central question of this study?

Does combining endurance and hypertrophic stimuli blunt the adaptations to both modalities and is this effect greater in muscles with larger baseline fibre cross sectional area?

What is the main finding and its importance?

Endurance exercise and hypertrophic stimuli can be combined to increase fatigue resistance and fibre size without blunting either adaptation regardless of baseline fibre size.

Previous studies have demonstrated that fibre cross‐sectional area (FCSA) is inversely related to oxidative capacity, which is thought to be determined by diffusion limitations of oxygen, ADP and ATP. Consequently, it is hypothesised that (1) when endurance training is combined with a hypertrophic stimulus the response to each will be blunted, and (2) muscles with a smaller FCSA will show a larger hypertrophic response than those with a large FCSA. To investigate this, we combined overload with endurance exercise in 12‐month‐old male mice from three different strains with different FCSA: Berlin High (BEH) (large fibres), C57BL/6J (C57) (normal‐sized fibres) and Berlin Low (BEL) (small fibres). The right plantaris muscle was subjected to overload through denervation of synergists with the left muscle acting as an internal control. Half the animals trained 30 min per day for 6 weeks. The overload‐induced hypertrophy was not blunted by endurance exercise, and the exercise‐induced increase in fatigue resistance was not impaired by overload. All strains demonstrated similar absolute increases in FCSA, although the BEH mice with more fibres than the C57 mice demonstrated the largest increase in muscle mass and BEL mice with fewer fibres the smallest increase in muscle mass. This study suggests that endurance exercise and hypertrophic stimuli can be combined without attenuating adaptations to either modality, and that increases in FCSA are independent of baseline fibre size.
New Treatment for Improving the Productivity of Shale Reservoirs Using Thermochemical Fluids
Authors: Hassan Amjed , Mahmoud Mohamed , Al-Majed Abdulaziz , Alade Olalekan , Mokheimer Esmail M. A. , Al-Nakhli Ayman
Published: November 2020

Shale reservoirs are characterized with very low productivity due to the high capillary pressure and the ultra-low rock permeability. This article presents an effective treatment to improve the hydrocarbon productivity for shale reservoirs by injecting thermochemical fluids. In this study, several measurements were carried out to determine the effectiveness of the presented treatment. Coreflood, rate transient analysis (RTA), and nuclear magnetic resonance (NMR) measurements were performed. The gas productivity was estimated, before and after the treatment, utilizing the gas flowrates and the pressure drop across the treated rocks. The improvement in gas productivity due to thermochemical fluids was estimated by calculating the productivity index (PI) and the absolute open flow (AOF) before and after the chemical injection. Also, the changes in the pore size distribution, due to chemical injection, were studied using NMR measurements. Results showed that thermochemical treatment can improve the gas productivity by 44%, increase the AOF by 450%, and reduce the capillary pressure by 47%. Also, NMR measurements showed that fractures were induced in the shale rocks after the treatment, which will improve the shale productivity. Ultimately, this study introduces, for the first time, the use of thermochemical fluids to improve the hydrocarbon productivity for shale reservoirs.
Discontinuous Dynamics and Bifurcation for Morphing Aircraft Switching on the Velocity Boundary
Authors: Huang Jianzhe , Fu Xilin , Jing Zhongliang , Xing Siyuan
Published: November 2020

The concept of morphing aircraft was developed many decades ago, and many researches on the morphing aircraft such as stability and control have been published. As the point of view of the dynamic theory, the dynamic system of the morphing aircraft is consisted with multiple subsystems, and each subsystem represents the morphing aircraft with specific structure to fulfill a particular flight task. The switching process from one structure to another for such a morphing aircraft is considered to be smooth and stable, and the switching time is also assumed to be infinitely small. In this paper, a morphing aircraft with high-speed structure, intermediate-structure and low-speed structure is studied. Such a morphing aircraft is set to switch between high-speed structure and low-speed structure when the speed of aircraft arrives a preset critical speed, and the analytical conditions for switchability is developed. If such a morphing aircraft cannot switch to a low-speed structure or high-speed structure at the moment when it arrives the critical speed, it will switch to an intermediate-structure and control to keep the speed remain constant. The analytical conditions for onset and vanish of such a morphing aircraft switching to the intermediate-structure are also provided. Mapping structure is defined to describe the periodic motions of such a morphing aircraft. The bifurcation scenario is calculated to show the complexity of such a hybrid dynamical system. A periodic motion is given to illustrate the flow of such a morphing aircraft switching on the velocity boundary.
Modified Model-Free Adaptive Predictive Control Applied to Vibration Reduction of Mechanical Flexible Systems
Authors: Pham Hoang Anh , Söffker Dirk
Published: November 2020

Model predictive control (MPC) has become more attractive in control engineering for the last decades because of its efficiency and robustness. In this paper, an effective control strategy is proposed for vibration reduction of mechanical flexible systems in which establishment of a global dynamic model of the controlled system is not necessary. A modified model-free adaptive predictive controller is designed by combination of MPC and model-free control theory. The novel idea of this contribution is that by using the compact-form dynamic linearization technique, the upcoming system outputs within a specified prediction horizon can be predicted in sequence. The data-based prediction model of the system only requires input/output information, and therefore the future control input increments as well as the unknown system parameters called pseudo-jacobian matrix can be estimated. To improve parameter estimation accuracy, another online estimation method namely recursive least-squares algorithm is applied instead of using the conventional projection algorithm. The control performance is verified nummerically for vibration control of a flexible ship-mounted crane represented as a multi-input multi-output (MIMO) system. Simulation results indicate that significant reduction of the crane oscillations and better control performance are observed when using the proposed controller in comparison with other traditional methods.
The Adjoint Gradient Method for Time-Optimal Control of a Moon Landing: Ascent, Descent, and Abort
Authors: Eichmeir Philipp , Nachbagauer Karin , Steiner Wolfgang
Published: November 2020

This article illustrates a novel approach for the determination of time-optimal controls for dynamic systems under observance of end conditions. Such problems arise in robotics, e.g. if the control of a robot has to be designed such that the time for a rest-to-rest maneuver becomes a minimum. So far, such problems have been considered as two-point boundary value problems, which are hard to solve and require an initial guess close to the optimal solution. The aim of this contribution is the development of an iterative, gradient based solution strategy for solving such problems. As an example, a Moon-landing as in the Apollo program, will be considered. In detail, we discuss the ascent, descent and abort maneuvers of the Apollo Lunar Excursion Module (LEM) to and from the Moon’s surface in minimum time. The goal is to find the control of the thrust nozzle of the LEM to minimize the final time.
Application of Munich Agile Concept for MBSE by Means of Automated Valet Parking Functions and the 3D Environment-Data
Authors: Salehi Vahid , Taha Jihad , Wang Shirui
Published: November 2020

In today’s complex world of development of functions for automating Driving Systems (ADS), methods, tools, systems and new approaches are necessary for a seamless application. Furthermore, it is important to apply new technics of simulation and visualization (Digital Twin) for the new ADS functions. To prototype and to test these functions in a physical manner is not only a costly and complex effort but also encounters legal and bureaucratic obstacles. The importance of simulation is very high. For that reason, this paper and corresponding research project will develop a consistent traceable System Engineering approach of autonomous driving functions and its environment based on Munich Agile Concept for Model-Based-Systems-Engineering (MBSE). MBSE is based on three important core pillar which is 1) Methods/Processes, 2) Language and 3) Systems. The purpose of the new developed Munich Agile Concept Approach is to handle the complexity over the entire ADS feature development from the system requirement definition process up to the test and validation of the system. The Munich Agile Concept contains six different levels which are System Requirement-, System Functional-, System Architecture-, System Validation-, System Test and the System-Usage-Level. For defining the first three-level, a graphical language called System Modelling Language (SysML) has been applied.
Metamaterial Design for Targeted Limb-Socket Interface Pressure Offloading in Transtibial Amputees
Authors: Brown Nathan , Owen Meredith K. , DesJardins John D. , Garland Anthony , Fadel Georges M.
Published: November 2020

While using a prosthesis, transtibial amputees can experience pain and discomfort brought on by large pressure gradients, at the interface between the residual limb and prosthetic socket. Current prosthetic interface solutions attempt to alleviate these pressure gradients by using soft homogenous liners to reduce and distribute pressures. This research investigates an additively manufactured metamaterial inlay with adjustable mechanical response in order to reduce peak pressure gradients around the limb. The inlay uses a hyperelastic behaving metamaterial (US10244818) comprised of triangular pattern unit cells which can be 3D printed with walls of various thicknesses controlled by draft angles. The hyperelastic material properties are modeled using a third order representation based on Yeoh 3rd order coefficients. The 3rd order coefficients can be adjusted and optimized to represent a change in the unit cell wall thickness to create an inlay that can meet the unique offloading needs of an amputee. Finite element analyses evaluated the pressure gradient reduction from: 1) A common homogenous silicone liner, 2) A prosthetist’s inlay prescription that utilizes three variations of the metamaterial, and 3) A metamaterial solution with optimized Yeoh 3rd order coefficients. When compared to a traditional homogenous silicone liner for two unique limb loading scenarios, the prosthetist prescribed inlay and optimized material inlay can achieve equal or greater pressure gradient reduction capabilities. These results show the potential feasibility of implementing this metamaterial as a method of personalized medicine for transtibial amputees by creating customizable interface solution to the meet unique performance needs of an individual patient.
Eight-Cable Robocrane Extension for NASA JSC ARGOS
Authors: Williams Robert L. , Graf Eric
Published: November 2020

This paper presents extension of the triangular 6-cable NIST RoboCrane to a rectangular 8-cable-suspended robot, motivated by an application in the ARGOS (Active Response Gravity Offload System) Laboratory at NASA Johnson Space Center. Six candidate cable/platform design arrangements are considered and evaluated in MATLAB simulation, based on all-eight-cable-positive tensions workspace, singularities, magnitude and slope of cable tensions during trajectories, translational/rotational stiffness, and cable interference. As ever in engineering design, there are tradeoffs, and recommendations are made as to the most suitable design out of the six candidates.
Comparison of Exams and Design Practica for Assessment in First Year Engineering Design Courses
Authors: Nolte Hannah , Berdanier Catherine , Menold Jessica , McComb Christopher
Published: November 2020

In response to calls for engineering programs to better prepare students for future careers, many institutions offer courses with a design component to first-year engineering students. This work proposes that traditional exam-based assessments of design concepts are inadequate, and alternative forms of assessment are needed to assess student learning in design courses. This paper investigates the self-efficacy differences between a traditional exam and a two-part practicum as a mid-semester assessment for introductory engineering students enrolled in a first-year design course. Increased self-efficacy has been linked to various positive student outcomes and increased retention of underrepresented students. The practicum consisted of an in-class team design task and an out-of-class individual reflection, while the exam was a traditional, individual written exam. All students completed a pre-assessment survey and a post-assessment survey, both of which included measures of design self-efficacy. Analysis showed that the practicum increased the design self-efficacy of students more effectively than the exam. Students who identified as women had greater gains in design self-efficacy during the practicum as compared to men. Identifying as a minority subgroup student was also trending towards being a significant predictor of change in self-efficacy for the practicum. Findings suggest that a mid-semester practicum is a successful assessment of design competencies that contributes to increased first-year engineering student self-efficacy.
Design of a Flexure Based Low Frequency Foucault Pendulum
Authors: Fluckiger Patrick , Vardi Ilan , Henein Simon
Published: November 2020

The Foucault pendulum is a well-known mechanism used to demonstrate the rotation of the Earth. It consists in a pendulum launched on linear orbits and, following Mach’s Principle, this line of oscillation will remain fixed with respect to absolute space but appear to slowly precess for a terrestrial observer due to the turning of the Earth. The theoretical proof of this phenomenon uses the fact that, to first approximation, the Foucault pendulum is a harmonic isotropic two degree of freedom (2-DOF) oscillator. Our interest in this mechanism follows from our research on flexure-based implementations of 2-DOF oscillators for their application as time bases for mechanical timekeeping.

The concept of the Foucault pendulum therefore applies directly to 2-DOF flexure based harmonic oscillators. In the Foucault pendulum experiment, the rotation of the Earth is not the only source of precession. The unavoidable defects in the isotropy of the pendulum along with its well-known intrinsic isochronism defect induce additional precession which can easily mask the precession due to Earth rotation. These effects become more prominent as the frequency increases, that is, when the length of the pendulum decreases. For this reason, short Foucault pendulums are difficult to implement, museum Foucault pendulum are typically at least 7 meters long. These effects are also present in our flexure based oscillators and reducing these parasitic effects, requires decreasing their frequency.

This paper discusses the design and dimensioning of a new flexure based 2-DOF oscillator which can reach low frequencies of the order of 0.1[Hz]. The motion of this oscillator is approximately planar, like the classical Foucault pendulum, and will have the same Foucault precession rate. The construction of a low frequency demonstrator is underway and will be followed by quantitative measurements which will examine both the Foucault effect as well as parasitic precession.
Anechoic Stubs As a Means for Damping Frame Vibrations: Analysis Using an Exact Wave-Based Approach
Authors: Lv Hangyuan , Leamy Michael J.
Published: November 2020

This paper explores the addition of small stubs with anechoic terminations (termed herein ‘anechoic stubs’) as means for damping and/or removing vibration modes from planar frame structures. Due to the difficulties associated with representing anechoic boundary conditions in more traditional analysis approaches (e.g., analytical, finite element, finite difference, finite volume, etc.), the paper employs an exact wave-based approach, incorporating Timoshenko beams, in which an anechoic boundary is simply represented by a zero reflection matrix. Several numerically-evaluated examples are presented documenting novel effects anechoic stubs have on the vibration modes of a two-story frame, such as eliminated, inserted and exchanged mode shapes. Modal damping ratios are also computed as a function of the location and number of anechoic stubs, illustrating optimal locations as a function of mode number. Forced vibration studies are then carried-out, demonstrating reduced, eliminated, and inserted resonance response.
Individual Differences in Describing Levels of Automation
Authors: Wentzky Chase , Summers Joshua D.
Published: November 2020

Level of automation (LoA) is increasingly recognized as an important principle in improving manufacturing strategies. However, many automation decisions are made without formally assessing LoA and can be made based on a host of organizational factors, like varied mental models used by managers in decision-making. In this study, respondents (N = 186) were asked to watch five different assembly tasks being completed in an automotive manufacturing environment, and then identify “how automated” or “how manual” they perceived the task to be. Responses were given using a visual analogue scale (VAS) and sliding scale, where possible responses ranged from 0 (totally manual) to 100 (totally automated). The activity explored how and when individuals recognized the automated technologies being employed in each task. The tasks of the videos varied primarily by whether the human played active or passive role in the process. Focus group comments collected as a part of the study show how rating patterns revealed functional systems-level thinking and a focus on cognitive automation in manufacturing. While the video ratings generally followed the LoA framework discussed, slight departures in the rating of each video were found.
Topology Optimization for Stiffened Panels: A Ground Structure Method
Authors: Gamache Jean-François , Vadean Aurelian , Dodane Nicolas , Achiche Sofiane
Published: November 2020

Reducing the weight of structures remains a major challenge in the aviation industry in order to reduce fuel consumption. The stiffened panel is the main assembly method for primary structures in aircraft, e.g. fuselage or wing.

Density-based topology optimization has been used in research and in industry as a tool to help create new stiffening patterns for aircraft components, such as ribs, spars, bulkheads or even floor design.

One critical aspect of stiffened panel design for wing structures is the buckling resistance. However, most work found in the literature does not include buckling analysis during optimization which leads to sub-optimal results when the stiffening layout is validated for buckling.

Including buckling as a constraint for the density-based topology optimization has proven to be a complex task, mainly caused by the fact that the buckling of the stiffeners is not captured accurately. As such, this work presents an optimization method for stiffened panels based on the ground structure approach usually used for truss topology optimization. The main novelty of the method is the use of a stiffener activation variable (SAV) to activate only one variable at a time, either the height or density variable associated with each stiffeners of the ground structure.

This work shows that while ground structure topology optimization requires more setup time and limiting the degrees of freedom of the optimization, it finds the best stiffening layout efficiently when compared to the density method.
The Value of Prototyping: An Investigation of the Relationship Between the Costs of Prototyping, Perceived Value, and Design Outcome
Authors: Nelson Jacob , Menold Jessica
Published: November 2020

Prototyping is an important part of the design process and has repeatedly been identified in prior work as an important tool for designers to test assumptions, communicate ideas, and develop design knowledge. Researchers, however, currently have a limited understanding of how the resources invested in a prototype influence designers’ decision-making and their perceptions of a prototype’s value. Prior work has shown that significant investment of time or money in a prototype can lead to undesirable effects such as design fixation, but the full impact of these factors on designers’ perceived value of the prototypes remains unclear. Likewise, it is unclear how prototype usage impacts the evolution of designer knowledge. To explore these relationships, a study was performed in a 16 week-long design project involving 32 teams of mechanical engineering students. Results suggest that effective prototyping uncovered new design knowledge and limited uncertainty early in the design process, allowing teams to spend more time testing and iterating later in the design process. High-performing teams also reported final prototypes as less valuable for gathering new knowledge than their peers. Importantly, the study did not find any significant relationships between the cost of a prototype in terms of money and time, and the perceived value of that prototype. Nor were any significant relationships found between costs and final design outcomes. This work underscores the need for better methods to evaluate the value of prototyping efforts.
Influence of Conceptual Sketches on Variety, Typology, and Novelty of Elicited Requirements
Authors: Spivey Nick , Davenport Brian , Patel Akash , Ortiz Joshua , Summers Joshua D.
Published: November 2020

The generally accepted engineering design process involves generating requirements prior to developing concepts. Despite this, educators often observe that student engineers tend to have ideas for the eventual solution even before fully defining the problem. Thus, a method of exploiting this natural proclivity may result in a better overall product or process. Coevolutionary design, in which a problem and its solution are developed interdependently, may provide a theoretical construct for such a method. It may be that allowing for the creation of sketches as a first step may improve the resulting requirements, which in turn would enhance the result. To test this, an experiment was developed to observe the effects of rearranging the design sequence to use an early conceptual sketch in the elicitation of constraints and criteria. Requirements were generated by third- and fourth-year mechanical engineering students and were subsequently analyzed based on their variety, typology, and novelty. It was found that the use of a preliminary conceptual sketch had a significant (positive) effect on the typology and novelty of the resulting requirements (α = 0.05), though no change in their variety was observed. Also, an additional intermediate step of identifying key features in the sketch further influenced requirement characteristics. The findings of this study support the coevolutionary model of design and suggest that the sketching of ideas and the identification of features in advance of listing requirements may be a valid design practice in the future. By creating an initial concept sketch and then distinguishing the important aspects of that sketch, engineers would be able to extract applicable requirements which they find inherent in their initial ideas. Finally, this method can align more naturally with the approach that many students employ in design. Rather than modifying behaviors, this method can exploit student behaviors to positive effect.
Three-Dimensional Symmetric Maximum Weight Lifting Prediction
Authors: Zaman Rahid , Xiang Yujiang , Cruz Jazmin , Yang James
Published: November 2020

Lifting heavy weight is one of the main reasons for manual material handling related injuries which can be mitigated by determining the limiting lifting weight of a person. In this study, a 40 degrees of freedom (DOFs) spatial skeletal model was employed to predict the symmetric maximum weight lifting motion. The lifting problem was formulated as a multi-objective optimization (MOO) problem to minimize the dynamic effort and maximize the box weight. An inverse-dynamics-based optimization approach was used to determine the optimal lifting motion and the maximum lifting weight considering dynamic joint strength. The predicted lifting motion, ground reaction forces (GRFs), and maximum box weight were shown to match well with the experimental results. It was found that for the three-dimensional (3D) symmetric lifting the left and right GRFs were not same.
A Test Rig for the Accurate Measurement of Bicycle Tyres Characteristics
Authors: Ballo Federico , Gobbi Massimiliano , Mastinu Giampiero , Previati Giorgio
Published: November 2020

In this paper, a new test rig for measuring the characteristics of bicycle tyres is presented. The test rig is designed to measure the parameters of a wide range of bicycle tyres, including race bicycles, mountain-bikes and city-bikes. The test rig consists of a frame that allows a single wheel to be cambered and steered. Electric motors can be added to produce longitudinal slip. The test rig is conceived to be employed either on a drum or on a flat surface. The friction on the drum or on the flat surface can be varied in a relatively easy way.

The test rig can measure the vertical force, the lateral force, the self aligning torque, the moment around the longitudinal axis, and, after proper arrangement, the longitudinal force. The steering and camber axles of the test rig intersect at the centre of the contact patch. In this way, the vertical vibrations of the wheel cause a pure vertical motion of the centre of the contact patch i.e. without longitudinal velocity. The lateral force is measured by a Watt’s linkage. The steering motion is allowed by pneumatic bearings, which guarantee a vanishing friction moment and thus an accurate measurement of the self-aligning moment. Some measured tyre characteristics are provided.
Modal Reduction Procedures for Flexible Multibody System Applications
Authors: Scapolan Matteo , Shan Minghe , Bauchau Olivier A.
Published: November 2020

The comprehensive simulation of flexible multibody systems calls for the ability to model various types of structural components such as rigid bodies, beams, plates, and kinematic joints. Modal components test offer additional modeling versatility by enabling the treatment of complex, three-dimensional structures via modal reduction procedures based on the small deformation assumption. In this paper, the problem is formulated within the framework of the motion formalism. The kinematic description involves simple, straightforward frame transformations and leads to deformation measures that are both objective and tensorial. Derivatives are expressed in the material frame, which results in the remarkable property that the tangent matrices are independent of the configuration of the modal component with respect to an inertial frame. This implies a reduced level of geometric nonlinearity as compared to standard description. In particular, geometrically nonlinear problems can be solved with the constant tangent matrices of the reference configuration, without re-evaluation and re-factorization.
Temporal Fault Injection Considerations in Resilience Quantification
Authors: Hulse Daniel , Hoyle Christopher , Tumer Irem Y. , Goebel Kai , Kulkarni Chetan
Published: November 2020

Resilience models assess a system’s ability to withstand disruption by quantifying the value of metrics (e.g. expected cost or loss) over time. When such a metric is the result of injecting faults in a dynamic model over an interval of time, it is important that it represent the statistical expectation of fault responses rather than a single response. Since fault responses vary over fault injection times, representing the statistical expectation of responses requires sampling a number of points. However, fault models are often built around computationally expensive dynamic simulations, and it is desirable to be able to iterate over designs as quickly as possible to improve system resilience. With this in mind, this paper explores approaches to sample fault injection times to minimize computational cost while accurately representing the expectation of fault resilience metrics over the set possible occurrence times. Two general approaches are presented: an a priori approach that attempts to minimize error without knowing the underlying cost function, and an a posteriori approach that minimizes error when the cost function is known. Among a priori methods, numerical integration minimizes error and computational time compared to Monte Carlo sampling, however both are prone to error when the metric’s fault response curve is discontinuous. While a posteriori approaches can locate and correct for these discontinuities, the resulting error reduction is not robust to design changes that shift the underlying location of discontinuities. The ultimate decision to use an a priori or a posteriori approach to quantify resilience is thus dependent on a number of considerations, including computational cost, the robustness of the approximation to design changes, and the underlying form of the resilience function.
Analysis and Study of Variable Stiffness Joints Based on Bi-Material Nested Elastomers
Authors: Sun Wei , Yu Jingjun , Cai Yueri
Published: November 2020

Variable stiffness joints are a kind of compliant mechanisms which can improve the safety of physical human-robot interaction which has attracted much attention in recent years. Elastic elements are used in the internal kinematic structures of variable stiffness joints. In this paper, Elastomers with magneto-rheological fluids (MRFs) properties have great potential application for variable stiffness joints (VSJs) and implantable bioelectronics devices by allowing actuators to rapidly and reversibly changed from a “fluid” to a “solid-like” state and precisely controlled within a very short time and over a wide range under a magnetic field. A new adjustable stiffness composites (ASCs) that combine an outside liner (PDMS) with a chamber (MRFs) is introduced. When improving the magnetic field intensity, the MRFs hardens and the stiffness increases by as much as 4–5 orders of magnitude. In order to solve the bi-material nested cantilever beam subjected to a concentrated tangential force at the free end of the beam, a theoretical approach is proposed by means of the Airy stress function method together with the stress function test solution. By comparing the results obtained from the theoretical and experimental measurements, a very good agreement is found, showing the accuracy and feasibility of the theoretical results. This solution will be useful in analyzing cantilever beam with arbitrary variations of bi-material nested and it can serve as a basis for establishing stiffness and stress theories. Due to the highly deformable of the ASCs, it has great potentially for our future soft robot design and manufacture work.
Uncertainty-Based Multidisciplinary Design Optimization for Feedback-Coupled Systems Under Both Parametric and Metamodeling Uncertainties
Authors: Liu Zhao , Song Zhouzhou , Zhu Ping , Xu Can
Published: November 2020

Uncertainty-based multidisciplinary design optimization (UMDO) is an effective methodology to deal with uncertainties in the engineering system design. In order to shorten the design cycle and improve the design efficiency, the time-consuming computer simulation models are often replaced by metamodels, which consequently introduces metamodeling uncertainty into the UMDO procedure. The optimal solutions may deviate from the true results or even become infeasible if the metamodeling uncertainty is neglected. However, it is difficult to quantify and propagate the metamodeling uncertainty, especially in the UMDO process with feedback-coupled systems since the interdisciplinary consistency needs to be satisfied. In this paper, a new approach is proposed to solve the UMDO problem for the feedback-coupled systems under both parametric and metamodeling uncertainties. This approach adopts the decoupled formulation and it applies the Kriging technique to quantify the metamodeling uncertainty. The polynomial chaos expansion (PCE) technique is applied to propagate the two types of uncertainties and represent the interdisciplinary consistency constraints. In the optimization approach, the proposed method uses the iterative construction of PCE models for response means and variances to satisfy the multidisciplinary consistency at the optimal solution. The proposed approach is verified by a mathematical example and applied to the fire satellite design. The results demonstrate the proposed approach can solve the UMDO problem for coupled systems accurately and efficiently.
Reliability Analysis and Random Vibration of Nonlinear Systems Using the Adjoint Method and Projected Differentiation
Authors: Papadimitriou Dimitrios , Mourelatos Zissimos P. , Hu Zhen
Published: November 2020

This paper proposes a new methodology for time-dependent reliability and random vibrations of nonlinear vibratory systems using a combination of a time-dependent adjoint variable (AV) method and a projected differentiation (PD) method. The proposed approach is called AV-PD. The vibratory system is excited by stationary Gaussian or non-Gaussian input random processes. A Karhunen-Loeve (KL) expansion expresses each input random process in terms of standard normal random variables. The nonlinear equations of motion (EOM) are linearized using a Taylor expansion using the first-order derivatives of the output with respect to the input KL random variables. An adjoint approach obtains the output derivatives accurately and efficiently requiring the solution of as many sets of EOM as the number of outputs of interest, independently of the number of KL random variables. The proposed PD method then computes the autocorrelation function of each output process at an additional cost of solving as many sets of EOM as the number of outputs of interest, independently of the time horizon (simulation time). A time-dependent reliability analysis is finally performed using a KL expansion of the output processes and Monte Carlo Simulation (MCS). The number of solutions of the EOM scales only with the number of output random processes which is commonly much smaller than the number of input KL random variables. The efficiency and accuracy of the proposed approach is demonstrated using a four degree-of-freedom (DOF) half-car vibratory problem.