bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term restoration altered edaphic properties and soil microbial communities in forests: evidence from four plantations of southern China
Authors: Yu Qingshui , Hanif Abu , Rao Xingquan , He Jinhong , Sun Dan , Liu Suping , He Dan , Shen Weijun
Published: February 2021

Afforestation has been an important approach to mitigate land deterioration and biodiversity reduction. There are increasing interests in understanding the responses of soil microbial communities under long‐term forest restoration, since they play a crucial role in the mediation of ecosystem functions while interacting with plants. Here we examined the effects of four forests (Acacia species [AM], Eucalyptus species [EE], mixed coniferous species [MC], mixed native broadleaf species [NS]) after 35‐year restoration (1986–2015) on soil environmental factors and soil microbial communities. Our results showed that afforestation significantly increased soil organic carbon (SOC) and total N (TN) while decreasing soil pH. Among the four forest types, there were significant differences for TN and TK (total K) but not for pH, sSOC, and TP (total P). Bacterial species richness and phylogenetic diversity in Acacia forest significantly declined more than those of other forests, but those of fungal communities were remarkably higher in the Acacia forest. Both the bacterial and fungal communities' structure of each forest were strongly related to soil TK and TP. Besides, TK and SOC were primary edaphic properties that respectively affected the distribution pattern of bacterial and fungal communities in four forests. Network structures in AM and MC compared with EE and NS were more complex and closely linked, hence more resistant to extrinsic interference. Our results demonstrate that afforestation altered soil properties and microbial communities during long‐term restoration, which may provide insight into ecological restoration practices and biodiversity maintenance.
Modeling and Managing Poliovirus Risks: We are Where we are…
Authors: Thompson Kimberly M.
Published: February 2021

This introduction for the third special issue on modeling poliovirus risks provides context for the current status of global polio eradication efforts and gives an overview of the individual papers included in the issue. Although risk analysis continues to support the Global Polio Eradication Initiative (GPEI), efforts to finish the job remained off track at the beginning of 2020 and prior to the COVID‐19 pandemic, as discussed in the special issue. The disruptions associated with COVID‐19 occurring now will inevitably change the polio eradication trajectory, and future studies will need to characterize the impacts of these disruptions on the polio endgame.
Etiological profile of diarrhea in solid organ transplant recipients at a tertiary care center in Southern India
Authors: Vyas Viral Dineshchandra , Parameswaran Sarojini Ashok , Paramasivan Piramanayagam , Sankaranarayanan Krishnan , Palaniswamy Kallipatti Ramasamy , Mohan Arumugam T , Srinivas Usha , Dhus Ubal , Muthuswamy Hariharan , Revathy Marimuthu S , Natarajan Murugan , Karunakaran Premkumar , Venkatesh Seshadri , Mahalingam Preethi , Patel Ankit
Published: February 2021

Background

Diarrhea is one of the common gastrointestinal (GI) adverse events after solid organ transplantation. Diarrhea may be caused by infectious or non‐infectious etiology. The infectious etiology of diarrhea varies according to the location and duration of diarrhea. Non‐infectious etiologies include drugs, inflammatory bowel disease, neoplasia. The objective of this study was to evaluate the etiological profile of diarrhea in solid organ transplant recipients presenting to a tertiary care center in Southern India.

Methods

This was a retrospective analysis of prospectively collected data of all solid organ transplantation recipients referred to the Department of Medical Gastroenterology for evaluation of diarrhea from April 2012 till May 2014. All patients had stool evaluated by wet mount examination, modified acid fast (AFB) stain, trichrome stain, culture, and Clostridium difficile toxin assay. EDTA plasma was collected for quantitative Cytomegalovirus (CMV) detection by real‐time PCR. If the diarrhea was acute (<2 wk), and no etiological agent was identified, empirical antibiotic therapy was instituted and followed up. If persistent or chronic diarrhea (>2‐4 wk), endoscopic evaluation (upper GI endoscopy and/or colonoscopy with biopsies), depending on the clinical type of diarrhea was done. If no specific etiological diagnosis was established after endoscopic evaluation, breath test for SIBO and celiac serology were done. If no specific etiology was identified after the above investigations, dose of immunosuppressive drugs was reduced. If diarrhea responded to dose reduction, it was considered to be drug related.

Results

Fifty‐eight episodes of diarrhea occurred in 55 solid organ transplant recipients during the study period. Renal transplant recipients constituted the majority (70%). Most (79%) of patients included in the study had their transplant > 6 mo ago. Infective diarrhea was the etiology in 46%, drug‐related diarrhea in 29.3%. No specific etiology was identified in 22.4% of patients. Parasites accounted for 69% of all infective diarrhea. Stool evaluation was the main investigation in establishing diagnosis in acute diarrhea. Endoscopic evaluation was required in two thirds of patients to establish diagnosis in chronic diarrhea.

Conclusion

GI infections and drug‐related diarrhea were the common causes of diarrhea in solid organ transplant recipients. Parasites were the most common infectious etiology of diarrhea. Step‐wise evaluation was able to identify the etiology in ~ 77% of patients. Overall, 98% of diarrheal episodes resolved.
Cytomegalovirus antiviral stewardship in the COVID‐19 Era: Increasing complexity of prophylaxis and treatment and potential mitigation strategies
Authors: Jorgenson Margaret R. , Descourouez Jillian L. , Wong Cynthia , Strayer Jill R. , Parajuli Sandesh , Rice John P. , Redfield Robert R. , Smith Jeannina A. , Mandelbrot Didier A. , Saddler Christopher M.
Published: February 2021

Cytomegalovirus (CMV) infection is one of the most common and significant complications after solid organ transplant (SOT). Severe acute respiratory coronavirus 2 (SARS‐CoV‐2), which causes the novel betacoronavirus 2019 disease (COVID‐19), has become the first global pandemic in 100 years. The world's attention has turned to address this unanticipated development; however, the viral infection that has long plagued outcomes after solid organ transplantation still requires vigilance. With physical distancing as the key intervention to reduce the healthcare burden, and the unease related to healthcare contact within the transplant population given the associated morbidity and mortality of COVID‐19 in transplant recipients, providers have struggled to evaluate and streamline essential in‐person healthcare contact, including laboratory visits. Owing to this, the COVID‐19 pandemic has placed a significant strain on the delivery of CMV prophylaxis and treatment after solid organ transplantation. In this piece, we will describe issues our CMV antiviral stewardship service has encountered in the care of the transplant recipient with CMV during the this unprecedented time and share our expert opinion to approaches to providing optimal, evidenced based care during a pandemic associated with a seemingly unrelated viral infection.
Multi‐omics analysis to visualize the dynamic roles of defense genes in the response of tea plants to gray blight
Authors: Wang Shuangshuang , Liu Lu , Mi Xiaozeng , Zhao Shiqi , An Yanlin , Xia Xiaobo , Guo Rui , Wei Chaoling
Published: February 2021

Gray blight (GB) is one of the most destructive diseases of tea plants, causing considerable damage and productivity losses; however, the dynamic roles of defense genes during pathogen infection remain largely unclear. To explore the numerous molecular interactions associated with GB stress in tea plants, we employed transcriptome, sRNAome and degradome sequencing from 1 to 13 days post‐inoculation (dpi) at 3‐day intervals. The transcriptomics results showed that differentially expressed genes (DEGs) related to flavonoid synthesis, such as chalcone synthase (CHS) and phenylalanine ammonia‐lyase (PAL), were particularly induced at 4 dpi. Consistent with this, the contents of catechins (especially gallocatechin), which are the dominant flavonoids in tea plants, also increased in the leaves of tea plants infected with GB. Combined analysis of the sRNAome and degradome revealed that microRNAs could mediate tea plant immunity by regulating DEG expression at the post‐transcriptional level. Co‐expression network analysis demonstrated that miR530b‐ethylene responsive factor 96 (ERF96) and miRn211‐thaumatin‐like protein (TLP) play crucial roles in the response to GB. Accordingly, gene‐specific antisense oligonucleotide assays suggested that suppressing ERF96 decreased the levels of reactive oxygen species (ROS), whereas suppressing TLP increased the levels of ROS. Furthermore, ERF96 was induced, but TLP was suppressed, in susceptible tea cultivars. Our results collectively demonstrate that ERF96 is a negative regulator and TLP is a positive regulator in the response of tea plants to GB. Taken together, our comprehensive integrated analysis reveals a dynamic regulatory network linked to GB stress in tea plants and provides candidate genes for improvement of tea plants.
SEC6 exocyst subunit contributes to multiple steps of growth and development of Physcomitrella (Physcomitrium patens)
Authors: Brejšková Lucie , Hála Michal , Rawat Anamika , Soukupová Hana , Cvrčková Fatima , Charlot Florence , Nogué Fabien , Haluška Samuel , Žárský Viktor
Published: February 2021

Spatially directed cell division and expansion is important for plant growth and morphogenesis and relies on cooperation between the cytoskeleton and the secretory pathway. The phylogenetically conserved octameric complex exocyst mediates exocytotic vesicle tethering at the plasma membrane. Unlike other exocyst subunits of land plants, the core exocyst subunit SEC6 exists as a single paralog in Physcomitrium patens and Arabidopsis thaliana genomes. Arabidopsis SEC6 (AtSEC6) loss‐of‐function (LOF) mutation causes male gametophytic lethality. Our attempts to inactivate the P. patens SEC6 gene, PpSEC6, using targeted gene replacement produced two independent partial LOF (‘weak allele’) mutants via perturbation of the PpSEC6 gene locus. These mutants exhibited the same pleiotropic developmental defects: protonema with dominant chloronema stage; diminished caulonemal filament elongation rate; and failure in post‐initiation gametophore development. Mutant gametophore buds, mostly initiated from chloronema cells, exhibited disordered cell file organization and cross‐wall perforations, resulting in arrested development at the eight‐ to 10‐cell stage. Complementation of both sec6 moss mutant lines by both PpSEC6 and AtSEC6 cDNA rescued gametophore development, including sexual organ differentiation. However, regular sporophyte formation and viable spore production were recovered only by the expression of PpSEC6, whereas the AtSEC6 complementants were only rarely fertile, indicating moss‐specific SEC6 functions.
Other radical geographies: Tropicality and decolonisation in 20th‐century French geography
Authors: Ferretti Federico
Published: February 2021

This paper analyses the anticolonialist commitment of a group of French geographers who variously criticised French colonialism or directly contributed to decolonisation movements in Africa in the central decades of the 20th century. Based on the analysis of works and unpublished archives of these scholars and activists, I argue that their work can be considered as a specific French contribution to early critical and radical geographies, exposing the complexity and diversity that constitutes the plurality of geographical traditions, to be understood through their stories of political dissidence. I extend current scholarship analysing histories and theories around the movement of “radical geography” as well as geographers' works on decolonisation, postcolonialism, and anticolonialism, stressing the need for diversifying geographical research's standpoints beyond Western canons. I especially call for rediscovering other critical and radical geographical traditions from outside the Anglosphere, eventually French anticolonialist geographies, whose exponents directly collaborated with colleagues from the South, especially the Maghreb and Western Africa. Studying these traditions is indispensable to decolonise geography and make it more international, cosmopolitan, and activist. This paper also extends recent contributions demonstrating that, in imperial ages, geography showed more potentiality for inspiring political dissidence than was commonly believed.
Previous experience, experimentation and export survival: Evidence from firm‐product‐destination level data
Authors: Esteve‐Pérez Silviano
Published: February 2021

This paper explores the role of a firm's product and/or market export experience and experimentation for survival of new product‐destination export spells, using firm‐level Spanish customs data over the period 1997–2015. Previous research has documented a positive impact of experience on export survival. This paper contributes to the extant literature by unravelling the distinct effect on export survival of ongoing accumulated experience (i.e., from the start of a product‐destination export spell), previous product and/or destination‐market experience and experimentation (repetition of product‐destination relationships). We find that 60% of new product‐country export spells end during their first year. Thereafter, the hazard rate remarkably falls with their elapsed duration (i.e., age). Exporting a new product endures a higher risk than entering a new market. Besides, experimentation (repeated product‐destination combinations) and previous experience (especially at product rather than at destination level) significantly lower the exit hazard. The results are consistent with previous studies that suggest that sunk costs to enter markets are relatively high, while experimentation and learning are more relevant at product level.
Feasibility of applying nonthermal plasma for dairy effluent treatment and optimization of process parameters
Authors: Suresh Ramya , Rajoo Baskar , Chenniappan Maheswari , Palanisamy Manikandan
Published: February 2021

Dairy industry effluent will pollute the environment if not properly treated. In the present work, the feasibility of nonthermal plasma (NTP) for the treatment of dairy industry effluent is assessed. The effect of energy yield and plasma intensity on reduction of Chemical Oxygen Demand (COD) removal is investigated. Box–Behnken design (BBD) is employed to optimize the operating parameters such as initial pH (5–9), reaction time (4–8 h), effluent flow rate (10–90 ml/min) and applied voltage (20–30 kV) where COD and energy yield are taken as responses. The optimum condition for COD removal and energy yield is same with a pH of 9, effluent flow rate of 10 ml/min and applied voltage of 30 kVp‐p, whereas reaction time differs as 8 and 4 h, respectively. COD reduction of 52% indicates that NTP process is a promising technology for dairy effluent treatment.
Oxygenation pattern and compensatory responses to hypoxia and hypercapnia following bilateral carotid body resection in humans
Authors: Niewinski Piotr , Tubek Stanislaw , Paton Julian F. R. , Banasiak Waldemar , Ponikowski Piotr
Published: February 2021

Key points

Five years after bilateral carotid body resection (bCBR) performed in four patients, the absence of the hypoxic ventilatory response persisted, suggesting no compensatory regrowth.

Breathing hypoxic gas mixtures (15% and 12%) results in a lower (by ∼10%) minimal blood oxygen saturation () in bCBR patients compared to heart failure subjects (CHF) with intact peripheral chemoreceptors.

After bCBR, patients were characterized by a greater short‐term variability in during mild hypoxia in comparison to the CHF group.

The ventilatory response to hypercapnia was preserved following bCBR and was sufficient to maintain minimal at levels comparable to controls when combined with hypoxia.

Bilateral CBR – a novel treatment modality for sympathetically mediated diseases – should be used with caution due to the risk of significant desaturation even during mild hypoxia equivalent to that experienced during long‐haul air travel and high altitude.

Carotid body resection has been proposed as a novel treatment for sympathetically mediated diseases but the safety of bilateral carotid body resection (bCBR) for blood oxygenation during hypoxic stress (long‐haul flights or high altitude) remains uncertain. Also unknown is whether central ventilatory drive is sufficient to maintain adequate oxygen saturation when exposed to hypercapnia with concomitant hypoxia. Thus, we administered: 15% O2, 12% O2, 5% CO2/12% O2 and 5% CO2/95% O2 to a group of four patients with congestive heart failure (65 ± 2.9 years) in whom bCBR was performed 5 years earlier. Ventilatory, haemodynamic and blood oxygen saturation () responses were recorded non‐invasively and compared to control groups with intact peripheral chemoreceptors (both healthy and heart failure patients). First, we confirmed that the ventilatory response to hypoxia was eliminated in patients with bCBR, although the increase in cardiac output was preserved. Second, administration of hypoxic gas mixtures resulted in a larger decrease in and greater short‐term variability of the leading to a lower minimal for both hypoxia levels in the bCBR group compared to heart failure controls (82.5 ± 1.2% vs. 91.6 ± 2.3% for 15% O2 and 73.8 ± 4.0% vs. 83.7 ± 3.1% for 12% O2). Third, in bCBR patients the ventilatory response to hypercapnia was present and sufficient to maintain a minimal at a level comparable to heart failure controls following administration of 5% CO2/12% O2 (88.7 ± 4.2% vs. 91.1 ± 2.8%). We conclude that bCBR carries a risk of significant oxygen desaturation even during mild hypoxia. Despite preservation of central chemosensitivity, future studies should focus on unilateral CBR or on pharmacological modulation of peripheral chemosensitivity.
Feature-Based Assembly Design: Concepts and Design Environment
Authors: Bordegoni Monica , Cugini Umberto
Published: February 2021

The design of mechanical assemblies is mainly done after having modeled single parts. Most of the CAD systems are still weak for what concerns assembly. For example, they do not support the manipulation or the modification of the part geometry or the mating conditions once the assembly is made. The introduction of a feature-based approach in assembly design, successfully used in the design of single parts, would offer several advantages. This paper describes some results of the research work done within a project funded by the European Union aiming at extending the use of features, to help in the solution of assembly problems in the aeronautical applications.
Feature Visualization
Authors: Versluis Jan Wouter , Bronsvoort Willem F. , de Kraker Klaas Jan , Seebregts Kees
Published: February 2021

New techniques for visualizing feature models are presented. These do not only provide better geometric and spatial model insight than the standard display techniques, but also functional insight into a feature model by visualizing engineering information.

Geometry is visualized by combining shaded and line visualization techniques, resulting in clearer images.

Among the engineering information that is visualized are feature intersections, closure faces and feature parameters. This is done by explicitly displaying feature geometry instead of the geometry of the final shape only, and by displaying additional information in a model image.

Combined, these techniques provide powerful possibilities to visualize feature models.

The implementation uses specified feature and camera properties and a cellular geometric datastructure for generating images. The cellular data structure contains the feature geometry information required for feature visualization.
Feature Extraction and Operation Sequencing for Machining on Mill-Turns
Authors: Dutta Debaslsh , Kim Yong Se , Kim Youngjin , Wang Eric , Yip-Hoi Derek
Published: February 2021

An integrated system to support both product and manufacturing process design should be such that (1) the part design can be evaluated and redesigned based on manufacturability analysis and (2) the manufacturing processes can be selected efficiently and flexibly exploiting product information provided by part design representations.

In this paper, we describe the collaborative research of the University of Illinois at Urbana-Champaign (UIUC) and the University of Michigan (UM) in computer-aided process planning for mill-turn machining. The UIUC geometric reasoning system based on convex decomposition identifies the machining features and maps the negative feature volumes to machining process methods, and generates geometry-based machining precedence relations. The UM process planning system based on genetic algorithm determines machining process sequences and assignment to multiple spindles and turrets.
A Knowledge-Based Approach to Concurrent Design of Sheet Metal Forming Product and Process and its Preliminary Implementation
Authors: Yang Shiyong , Nezu Kikuo
Published: February 2021

This article deals with concurrent design of sheet metal forming product and process by using process modeling and knowledge-based approach. An inverse finite element algorithm and knowledge representation schemes are presented. Numeric models out of process modeling are integrated into knowledge base, with resort to a mathematical and graphical software MATLAB and to a supporting shell called “concurrent design environment” (CDE) developed in Common Lisp. The proposed system can make preliminary determination of product and process specifications such that the product is compatible with its targeted forming conditions with maximum material utilization ratio, shortest lead-time, and reliable quality.
The Application Protocol Information Base World Wide Web Gateway
Authors: Lubell Joshua
Published: February 2021

The Application Protocol Information Base (APIB) is an on-line repository of documents for the Standard for the Exchange of Product model data (STEP, officially ISO 10303 — Product Data Representation and Exchange). Document types in the APIB include STEP Application Protocols and Integrated Resources. Application Protocols are standards that are intended to be implemented in software systems, and Integrated Resources are used by them as building blocks. Application Protocols and Integrated Resources are represented in the Standard Generalized Markup Language (SGML) in the APIB in order to facilitate efficient information search and retrieval. This paper describes a World Wide Web gateway to the APIB, implemented using the Common Gateway Interface (CGI) standard. The APIB gateway allows STEP developers to efficiently search for ISO 10303 standards and supporting information. The only client software required to use the APIB gateway is a third party web browser.
VirTeam Tool
Authors: Hillmer Dirk
Published: February 2021

The rapid evolution of information and the new potentials for communication between people, have been of great importance to the success of most organizations. Key aspects were the increased availability of computer networks and the rowing trend towards team work.

People are becoming connected through the Internet. People can use the network behind their computer as a great resource for solving problems. The purpose of this research is to simplify starts of collaboration tools. Individuals will be able to establish connections on demand. The schedule of group appointments and conference schedule should be supported, therefore, all necessary information has to be provided. Also behind firewalls a secure way to allow access to these data has to be found.
A Generic Framework for Internet-Based Supply-Chain Interaction
Authors: Veeramani D. , Joshi S. M.
Published: February 2021

To remain competitive in the global marketplace, manufacturing companies are transforming their organizational structure and operational philosophy from one based on vertical-integration to one based on core competencies. This trend has resulted in an economy wherein practically every manufacturing company has become dependent on a supply-chain of vendors in order to serve its customers. In the context of this distributed manufacturing environment, the Internet and related technologies such as Java, VRML and intelligent WWW agents are creating fundamentally new approaches to supply-chain interactions that offer greater flexibility in identifying suppliers and the ability to dramatically reduce the response time within a supply-chain for processing requests-for-quotation (RFQs) and orders from customers. In this paper, we describe a generic framework for Internet-based customer-vendor interactions, and present a computer-integrated system for rapid and effective processing of RFQs in such an Internet-based supply-chain. We also identify some key research challenges within this framework that need to be overcome for Internet-based supply-chain interaction to be successful.
Case Studies on the Use of Virtual Reality for an Integrated Design and Manufacturing System
Authors: Angster Scott , Jayaram Sankar , Hutton David
Published: February 2021

Companies are being forced to create products at a highly accelerated rate and have turned to new design techniques such as virtual prototyping. One of the newest virtual prototyping tools is the use of virtual reality for design and manufacturing analysis. Many groups have developed systems that use virtual reality techniques such as virtual fly-throughs, simulations and three-dimensional visualization. Additionally, there is an increased amount of research in the area of human-integrated techniques or human-in-the-loop analysis using virtual reality. In the field of design and manufacturing, most work has either been in simulation or in the field of human interaction without the use of virtual reality. Although these provide valuable information, a system that couples human-interaction with virtual reality can provide more information than that provided by current computer-aided design and manufacturing software. One concern, however, is the accuracy of these systems and whether the data that is obtained from these systems can be utilized. This paper presents studies performed in a virtual environment for a design and manufacturing system.
Computer Aided Design of Rotary Screen and its Conveyor for Solid Waste Processing Systems
Authors: Kaftanoglu Bilgin , Alkan Okan
Published: February 2021

In this study, typical solid waste processing systems are analyzed. Then, a rotary screen and conveyor is designed for composting plants. A computer program is developed for the design procedure. By use of a simulation model included in the program, data are obtained and these are plotted to see system characteristics. These data then, are compared with the previous works.
Air Filter Pleat Flow Simulations With Monte Carlo Particle Deposition
Authors: Vickery Curtis M.
Published: February 2021

Automotive air filter pleat parameters must often be estimated by design engineers, affecting overall filter performance. This paper examines pressure-flow response of and particle deposition upon three different pleat profiles. Pleat models, analysis operating point, and analysis parameters were based on a Purolator automotive air filter application. Computational assumptions included steady state, incompressible, isothermal, laminar air flow with a modified/extended Darcy law equation used for media flow computations. Inlet velocities were set to maintain the filter rated volumetric flow rate with equal pressure drop through each pleat model.

1–50 micron diameter spherical particles were used in Monte Carlo particle deposition analyses. Once introduced into the computed flow fields, particle trajectories were computed assuming inertial, body, buoyancy, and drag forces were active. Histograms depicting particle starting and deposition locations were constructed for five particle size sub-classes. Flow field and structural influences on particle deposition tendencies were noted.
Geometric Tools Dedicated to the Adaption and Idealization of 3D Models for F.E. Analysis
Authors: Véron Philippe , Léon Jean-Claude
Published: February 2021

Geometric adaptions and idealizations of 3D models for F.E. analysis purposes are often necessary. Geometric tools are proposed to partly automatize shape adaptions and idealizations of polyhedral models. The simplification process is monitored using error zones attached to each polyhedron vertex. Their dimension may be either set by the designer, by an a posteriori or by an a priori mechanical mesh adaption process. Such an approach allows to process various polyhedral models characterized by general and complex shapes. A classification of nodes and edges is carried out to apply a specific node removal operator in accordance with the local geometric configuration around a node. Moreover, specific criteria are used to select the best candidate node for removal. Also, additional operators have been developed to process particular configurations and produce the final idealized model. During this geometric idealization process, the shape restitution of the part is maintained through an inheritance process of the error zones. Topological changes as well as the coherence of the non-manifold geometric model are managed using specific criteria to produce acceptable approximations of idealized geometries.
Modeling and Pressure-Based Force Control of a Hydraulic Actuator
Authors: Lyon Scott M. , Evans Mark S.
Published: February 2021

A dynamic model of a hydraulic actuator/spool valve combination is developed using the bond graph method. Feedback linearization is used to develop a force controller for the system using hydraulic pressure in each chamber of the actuator along with piston position and velocity as feedback. The use of a feedforward term to compensate for the seal friction within the actuator provides for a stable and accurate controller. Velocity control is achieved through calculation of the reference force required to overcome the seal friction and produce the acceleration required to reach the desired velocity. It is shown that the use of such a force controller allows for an acceptable transition from velocity to force control when the piston comes in contact with an external surface.
A Decomposition Approach for the Topological Synthesis of Articulated Gear Mechanisms
Authors: Chen Dar-Zen , Liu Chia-Pin
Published: February 2021

This paper presents an efficient methodology for the structural synthesis of articulated gear mechanisms. This approach is based on the idea that the kinematic structure of a articulated gear mechanism can be described by an equivalent open-loop chain and mechanical transmission lines and each mechanical transmission line by input and transmission units. A model is established to represent the hierarchical relation among subsystems. A link partition algorithm is also presented to decompose the constraints on the number of link in the decomposition process. According to the model and partition algorithm, a composition polynomial is derived to represent the typology decomposition relation within the desired mechanism with specified configuration and number of links. In the composition polynomial, subsystems in each level are defined symbolically with the distributed number of links and configuration. From the unit-level composition polynomial, unit combinations of the desired mechanism are indicated. Thus, suitable units can be selected from the former identified admissible units and combined upward along the hierarchical model according to the synthesis process. With the clear specification on the composition of the desired mechanism, admissible mechanisms can be enumerated efficiently and systematically.
Finding the Principal Axes of Screw Systems
Authors: Parkin Ian A.
Published: February 2021

The paper provides computational methods for determining the principal screws of an N-system of screws of the form S^=∑i=1NaiS^i,aireal when a basis of N, 2 ≤ N ≤ 5, linearly independent screws Ŝi has been provided.
Trimmed Free-Form Surfaces Submitted to Parametric Modelling
Authors: Guillet Stéphane , Léon Jean-Claude
Published: February 2021

A new parametric modelling approach focusing on trimmed free-form surfaces is introduced. The surface deformation process required is controlled through geometric constraints such as deforming the surface until it becomes tangent to a pre-defined plane.

Surfaces are bounded by trimming lines and use a multi-patch representation (i.e.: a B-Spline based model). The G1 continuity across the various surface patches is preserved during the deformation process. Therefore, the C0 and G1 continuities across trimmed surfaces boundaries can be correctly approximated by parametric constraints.

The surface deformation process uses an analogy between the mechanical equilibrium of a rigid bar network and the control polyhedron of free-form surfaces. The bar network parameters may be set up to achieve either isotropic or anisotropic surface deformations. The surface deformation may be located into an arbitrary shaped area to produce either a local or a global deformation.

Parametric modelling of trimmed free-form surfaces is subjected to non-linear geometric constraints. This problem resolution uses an optimization process which minimizes the shape changes of the surface area subjected to the parameters of the deformation process.

An example illustrates the behavior of the parametric modelling process applied to two trimmed surfaces under various sets of continuity and boundary conditions.
Features: Information Carriers for the Product Creation Process
Authors: Vajna Sándor , Wegner Britta
Published: February 2021

Computer-internal product description is limited to models consisting only of the geometry of a technical product and its components. The CAD modellers set up the geometry from elementary elements, which have no direct relation to their meaning for the real product and its production. Logical connections between geometry and important non-geometrical informations are missing. Many informations about the product are not stored and get lost when being modeled with present systems. Therefore CAD systems must provide more comprehensive functionalities than only possibility to describe the geometry of component parts and structural components.

One approach of a uniform representation of different product information is the introduction of features as information carriers, which allow a grouping of data belonging together not only by geometric relation. Features must be implemented in CAx systems for a most complete possible support of the design activities. Feature modelling does not replace known techniques, but improves and completes them.
Dynamic Modelling of a Three Degree-of-Freedom Planar Platform-Type Manipulator
Authors: Attia Hazem A. , Mohamed Maher G.
Published: February 2021

In this paper, the dynamic modelling of a planar three degree-of-freedom platform-type manipulator is presented. A kinematic analysis is carried out initially to evaluate the initial coordinates and velocities. The dynamic model of the manipulator is formulated using a two-step transformation. Initially, the dynamic formulation is written in terms of the Cartesian coordinates of a dynamically equivalent system of particles. Since there is no rotational motion associated with a particle, then the differential equations of motion are derived by applying Newton’s second law to study the translational motion of the particles. The constraint forces between the particles are expressed in terms of Lagrange multipliers. Then, the differential equations of motion are written in terms of the relative joint variables. This leads to an efficient solution and integration of the equations of motion. A numerical example is presented and a computer program is developed.
Power Loss Analysis and the Selection of a Most Efficient Clutching Sequence Associated With an Automatic Transmission Mechanism
Authors: Hsieh Hsin-I , Tsai Lung-Wen
Published: February 2021

This paper presents a methodology for the identification of a most promising clutching sequence associated with an epicyclic-type automatic transmission mechanism. First, a methodology for the analysis of torque distribution on the links of an epicyclic gear mechanism is described. Then, the power loss relations associated with various clutching sequences of an epicyclic gear mechanism are derived. Finally, a procedure for the selection of a most efficient clutching sequence associated with a transmission mechanism is developed.
Use of Penalty Function in Topological Synthesis and Optimization of Strain Energy Density of Compliant Mechanisms
Authors: Frecker Mary I. , Kota Sridhar , Kikuchi Noboru
Published: February 2021

A penalty function approach is used in conjunction with a multi-criteria optimization method for topology synthesis of compliant mechanisms. This method can help facilitate convergence to physically meaningful solutions for problems with a large number of design variables. The second part of the paper is an investigation of the element strain energy density of the optimal solution, where a second stage size optimization routine is developed. The solution from the topology optimization is used as a starting point for the resizing algorithm, which uses an optimality criteria method based on the overall average strain energy density. This second stage optimization more uniformly distributes the element strain energy densities in order to avoid localized areas of high stress or strain.
Automated Shape Optimization Using Parametric Solid Models and p-Adaptive Finite Element Analysis
Authors: Salagame Raviprakash R.
Published: February 2021

A shape optimization capability which is fully integrated with geometry data is developed in this paper. A key feature of the system is the direct use of parametric solid model as the primary design model for shape optimization. This choice leads to a tight coupling between optimization and geometry, a highly desirable feature for an automated design environment. The approach exploits the parametric engine of the solid modeler to update the geometry at the end of each iteration. Responses are generated using polyFEM, a p-adaptive solver supported by a fully automatic three dimensional p-element mesh generator. It is illustrated that the use of p-adaptive technology and parametrized solid model assist us in achieving a high degree of automation.
A Parametric Approach to the Optimization-Based Design of Compliant Mechanisms
Authors: Parkinson Matthew B. , Howell Larry L. , Cox Jordan J.
Published: February 2021

Several optimization-based strategies have been proposed for compliant mechanism design that do not rely on the experience or intuition of the designer. This paper demonstrates an optimization-based method wherein compliant mechanisms are modeled parametrically within an optimization and a finite element analysis package. Topological optimization is performed to minimize an objective function representing the fitness of the design. This methodology exploits the nonlinear nature of compliant mechanisms and augments optimization-based methods previously proposed.

Using this method, constant-force mechanisms optimized for a displacement from 4% to 25% of the mechanism’s total length were predicted to remain within 3.58% of constant force. Results from the testing of fabricated mechanisms are: for 4–25% displacement, within 7.5% constant force; for 18–65% displacement, within 2.3%. Path generation mechanisms were designed with similarly encouraging results.
Applying Virtual Reality Techniques to Sensitivity-Based Structural Shape Design
Authors: Yeh Tsung-Pin , Vance Judy M.
Published: February 2021

Virtual reality (VR) provides a design space consisting of three-dimensional computer images where participants can interact with these images using natural human motions in real time. In the field of engineering design, prototyping and design verification have provided the initial application areas for VR. The research presented in this paper takes the scenario one step further by incorporating free-form deformation techniques and sensitivity analysis into the virtual world such that the designer can easily implement analysis-based shape design of a structural system where stress considerations are important. NURBS-based free-form deformation (NFFD) methods and direct manipulation techniques are used as the interface between the VR interaction and the finite element model. Sensitivity analysis is used to allow the designer to change the design model and immediately view the effects without performing a re-analysis. An engine connecting rod is analyzed to demonstrate how virtual reality techniques can be applied to structural shape design.
Vibration of Nearly Perfect Spring Equilibrators
Authors: Soper R. Randall , Mook Dean T. , Reinholtz Charles F.
Published: February 2021

Perfect spring equilibrators balance an eccentric rotating weight over a wide range of motion. The mechanism relies on a spring of zero free length. One practical implementation uses a spring and cable of finite free length wrapped over a pulley located at the grounded spring attachment point of the ideal mechanism. The pulley of finite radius introduces some error in the balancing moment.

In this paper the kinematics of a practically implemented perfect spring equilibrator are developed. Two kinematic cases are shown to exist. In one case, the kinematics are periodic in the weight arm rotation. In the other case, the geometry causes the spring cable to wrap or unwrap resulting in non-periodic kinematics. Phase portraits are used to illustrate the nonlinear dynamics of the system. The effect of various parameters are examined.
Trust Region Augmented Lagrangian Methods for Sequential Response Surface Approximation and Optimization
Authors: Rodríguez José F. , Renaud John E. , Watson Layne T.
Published: February 2021

A common engineering practice is the use of approximation models in place of expensive computer simulations to drive a multidisciplinary design process based on nonlinear programming techniques. The use of approximation strategies is designed to reduce the number of detailed, costly computer simulations required during optimization while maintaining the pertinent features of the design problem. To date the primary focus of most approximate optimization strategies is that application of the method should lead to improved designs. This is a laudable attribute and certainly relevant for practicing designers. However to date few researchers have focused on the development of approximate optimization strategies that are assured of converging to a solution of the original problem. Recent works based on trust region model management strategies have shown promise in managing convergence in unconstrained approximate minimization. In this research we extend these well established notions from the literature on trust-region methods to manage the convergence of the more general approximate optimization problem where equality, inequality and variable bound constraints are present. The primary concern addressed in this study is how to manage the interaction between the optimization and the fidelity of the approximation models to ensure that the process converges to a solution of the original constrained design problem. Using a trust-region model management strategy, coupled with an augmented Lagrangian approach for constrained approximate optimization, one can show that the optimization process converges to a solution of the original problem. In this research an approximate optimization strategy is developed in which a cumulative response surface approximation of the augmented Lagrangian is sequentially optimized subject to a trust region constraint. Results for several test problems are presented in which convergence to a Karush-Kuhn-Tucker (KKT) point is observed.
Robot Manipulator Trajectory Synthesis for Minimal Vibrational Excitation
Authors: Kim W. , Rastegar J.
Published: February 2021

As a robot manipulator is forced to track a given trajectory, the required actuating torques (forces) may excite the natural modes of vibration of the system. Due to their nonlinear dynamics, internally and externally induced high harmonic excitation torques are generally generated even though such harmonics have been eliminated from the synthesized trajectories and filtered from the drive inputs. It is therefore desirable to synthesize trajectories such that the actuating torques required to realize them do not contain higher harmonic components with significant amplitudes. In this paper, a systematic method is presented for synthesizing such trajectories. With such trajectories, a robot manipulator can operate at higher speeds and achieve higher tracking accuracy with suppressed residual vibration. It is shown that in general and for a given starting point, such trajectories can only be synthesized to a portion of the operating space of the manipulator. The method is developed based on the Trajectory Pattern Method (TPM). The application of the method to optimal trajectory synthesis for a plane 2R manipulator is presented.
Trajectory Synthesis and Redundancy Resolution for High Speed Point to Point Motions of Redundant Robot Manipulators
Authors: Kim W. , Rastegar J.
Published: February 2021

Trajectory synthesis for robot manipulators with redundant kinematic degrees-of-freedom has been studied by numerous investigators. Redundant manipulators are of interest since the redundant degrees-of-freedom can be used to improve the local and global kinematic and dynamic performance of a system. As a robot manipulator is forced to track a given trajectory, the required actuating torques (forces) may excite the natural modes of vibration of the system. Noting that manipulators with revolute joints have nonlinear dynamics, high harmonic excitation torques are generally generated even though such harmonics have been eliminated from the synthesized trajectories and filtered from the drive inputs. In this paper, a redundancy resolution method is developed based on the Trajectory Pattern Method (TPM) to synthesize trajectories such that the actuating torques required to realize them do not contain higher harmonic components with significant amplitudes. With such trajectories, a robot manipulator can operate at higher speeds and achieve higher tracking accuracy with suppressed residual vibration. As an example, optimal trajectories are synthesized for point to point motions of a plane 3R manipulator.
Designing Dynamically Compensated and Robust Cam Profiles With Bernstein-Bézier Harmonic Curves
Authors: Srinivasan Lakshmi N. , Ge Q. Jeffrey
Published: February 2021

This paper deals with the problem of designing dynamically compensated cam profiles to minimize residual vibrations in high-speed cam-follower systems. The traditional Polydyne method is modified and extended to achieve significant improvement in residual vibration characteristics. First, cam displacement curves are represented by Bernstein-Bézier harmonic curves as opposed to polynomial curves. These recently developed harmonic curves are low in harmonic content and therefore the resulting cam profiles are less prone to induce resonant vibrations in the follower system. Second, the design procedure is expanded such that the residual vibrations of the resulting cam-follower system is not only extinguished at the design speed but also made insensitive to speed variations. Numerical examples are given in the end.