bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical investigation of introduction of HFQ® process manufacturing of A-pillar part
Authors: Lukacs Zsolt
Published: June 2021

To meet the challenges of the automotive industry in recent decades, engineers have responded with new advanced materials and new technological processes suitable to form the new materials. The appearance of aluminium and its alloys in the automotive industry was justified by its lower density compared to steels and by the weight reduction arising from it. The lower ductility of aluminium alloys with sufficient strength initiated the development of new innovative technology (HFQ®). This paper presents a numerical feasibility study using the AutoForm software system by comparing two technological processes, i.e. the Press Hardening of Steels (PHS®) vs. Hot Forming and Quenching (HFQ®) of aluminium alloys. The Thermo-Solver module of the AutoForm software system includes material card for the 22MnB5 steel grade but does not for the AA7075 high strength aluminium alloy. Therefore, the material parameters that are necessary for hot forming simulation by the AutoForm must be determined experimentally. For this purpose, the GLEEBLE 3500 thermo-mechanical simulator was used to determine the basic material properties with hot uniaxial tensile tests and hot formability tests were performed to determine the forming limits (FLC).
Die material properties needed for Hot Stamping of High Strength Sheet Materials
Authors: Sivertsen S , Oliver R
Published: June 2021

Industries performing hot forming of high strength sheets are constantly requesting improvements in aspects of die material to achieve a suitable die life and production efficiency. The die material performance to resist the upcoming failure mechanisms based on thermal or mechanical loading is crucial for production efficiency and competitiveness. Therefore, die material for hot stamping needs to have the correct combination of properties to resist upcoming failure mechanism such as cracking, premature wear and plastic deformation. Surface softening during heat exposure contributes to plastic deformation due to hardness loss and has shown to have a direct impact in the potential of wear resistance. The purpose of this paper is to present tool steel solutions from Uddeholms AB, which contains key properties within several fields of hot forming to increase production efficiency.
On appropriate Finite Element discretization in simulation of gas-based hot sheet metal forming processes
Authors: Baru N. K. , Teeuwen T. , Teller M. , Hojda S. , Braun A. , Hirt G.
Published: June 2021

Gaseous medium is being used for sheet metal forming at elevated temperatures, especially for lightweighting purposes. These processes enable forming of high strength alloys of a wide range of thickness due to low material flow stress as well as improved formability. In these processes, the resulting component properties are an interplay of numerous parameters. Instead of cost and time intensive experiments, FEM aids an effective and economic process optimization and enables a better understanding of the influence of process parameters on the component properties. In the current study, the importance of appropriate discretization of the workpiece within a gas-based hot sheet metal forming process is investigated based on a laboratory scale component. AA6010 sheet metal blanks of different thicknesses are studied numerically and experimentally. Simulations with different types of elements are performed and the evolution of process parameters as well as their influence on the final component thickness are analysed. Different element types resulted in noticeable difference in the simulation results and this difference also varies with the initial sheet thickness. Upon further experimental validation, the suitable element type for workpiece discretization is suggested, which enables practitioners to get reliable results via FE simulation of these processes.
Enhancement of springback prediction of AHSS parts by advanced friction modelling
Authors: Durmaz U , Heibel S , Schweiker T , Merklein M , Berahmani S , Hol J , Naegele P
Published: June 2021

The complex springback behaviour of advanced high strength steel parts makes a robust manufacturing process challenging, mainly in terms of part dimensional accuracy. Therefore, an accurate springback prediction using sheet metal forming simulation is of a great importance to realize reliable forming processes and to achieve the target geometry. An accurate springback prediction requires an exact computation of the elastic stresses from the plastic deformations, which can be influenced among others by the retention of the sheet metal and the frictional properties of the parts. However, the frictional behaviour in the forming process has been often simplified by using a constant friction coefficient in the simulation, which could lead to a significant deviation in the springback prediction. To address this limitation, TriboForm software provides an advanced friction model in which friction is a function of several process setting parameters, namely pressure, strain, temperature and velocity. In this contribution, the advanced friction models for DH800 and CP800 materials are generated. Compared to a constant friction coefficient of 0.15, it is found that the prediction of flange angle of deep drawn hat profiles, produced by several blank holder forces, can increase up to 70% and of the sheet’s draw-in up to 10%.
Compensating the springback of ultra-high-strength steel parts by specific stress superposition during sheet metal forming
Authors: Radonjic R , Liewald M
Published: June 2021

Ultra-high-strength steel sheets offer considerable advantages in car body construction regarding the permanent requirements for vehicle weight reduction as well as the increase in crashworthiness of sheet metal parts. However, when forming such sheet metal materials, the main problem relates to their distinctive springback behaviour, which occurs after the formed part has been released. This paper shows a methodology for springback compensation based on the superposition of stresses acting in the meridian direction of the formed sheet metal part. These stress superposition effects are induced via the tool radii by alternating blank draw-in during deep drawing. As a result, the workpiece areas contacting the punch radii during the deep drawing process are subjected to repeated bending and unbending. In order to analyse occurring stress superposition effects and their influence on springback appearance, simulation was performed using the FE-code LS-Dyna. Furthermore, an optimal blank draw-in kinematic could be defined using the forming simulation, which significantly reduced springback of a double-curved hat-shaped component made of DP 980 steel sheet after forming. Finally, this numerically determined methodology for springback compensation has been experimentally proved using tool that enables alternating blank draw-in during sheet metal forming.
Structural springback analysis of car body closure assemblies using finite element process chain simulations
Authors: Schuler F. , Liewald M.
Published: June 2021

In recent decades, numerical simulation methods have become increasingly important in car body engineering to achieve the high dimensional quality requirements for closure assemblies like bonnets, doors and tailgates. In order to model the entire manufacturing process, latest research works have been focusing on combining the finite element-based simulation models. These complete process chain simulations are able to predict the springback behaviour of the assembly before the physical realization of the tools and processes. The purpose of this study is to introduce a method to use finite element process chain simulations to analyse the structural springback behaviour of car body closure assemblies. Therefore, the numerical process chain simulations are combined with statistical and stochastic tools in order to develop a meta-model, which represents the dimensional accuracy of the investigated assembly. The presented method will then be schematically advanced to be ultimately used in different application areas like robustness and tolerance analyses.
A critical assessment of notched tensile tests for formability mapping of AHSS sheets
Authors: Wagner L. , Larour P. , Sonnleitner F. , Felbinger A. , Angeli J.
Published: June 2021

The influences of specimen geometry during the determination of local ductility have recently been investigated, using the fracture surfaces of standardized tensile tests specimens. Among the shortcomings of these specimens was the rather undefined strain path to failure, i.e. uniaxial tension followed by a deviation towards a more or less pronounced plane strain path, and the varying fracture angle, often hampering accurate image acquisition of the fracture surface. Notched tensile tests are currently used during damage model calibration for sheet metal for crash simulation. These samples exhibit a defined strain path to fracture and the notch triggers fracture predominantly perpendicular to the tensile direction. These kind of specimens have therefore been suggested as alternative to standardized tensile test specimens. However, several issues need to be addressed for notched tensile specimens as well, in addition to being an undesired additional test during e.g. quality control. These include again geometric considerations as well as the effect of different fracture types on the resulting measures of local fracture strain.
Alternative characterization method for the failure behavior of sheet metals derived from Nakajima test
Authors: Kohl D , Merklein M
Published: June 2021

One sustainability approach in sheet metal forming is to reduce costs by increasing the reliability of the forming process by applying numerical simulations. These are based upon the finite element analysis and require specific characteristic values of the material. To improve the accuracy of the numerical model regarding the failure behavior, forming limit curves (FLC) which display the conduct and failure boundaries of sheet metals are characterized. Optical measurement systems are used to analyze the strain distribution and to generate a material dependent FLC. To reduce the amount of testing, the tensile test, the plane-strain test and the hydraulic bulge test are combined to characterize the uniaxial, plane, and the biaxial strain area and the forming limit. The results are summarized in the presented FLC, which is consequently compared with results from the standardized Nakajima test. The method is validated with different materials to compare a ductile (DX54D), a brittle (DP800) and a lightweight sheet metal (AA5182). That approach is used for the validation of the alternative and cost-effective FLC characterization. This eliminates the need for the Nakajima testing facility and the high utilization of a testing machine can save costs and time in creating the specific material data.
Study on the impact of temperature on the warm bending of aluminium alloy sheets
Authors: Mauduit A , Maillard A
Published: June 2021

Warm forming of aluminum is a recent process and its developments have been mainly focused on drawing. This study takes a look at bending, a process widely used in industry. After the 2017A T4 and 6061 T6 aluminum alloys are characterized at both room and warm temperatures, bending of these materials is carried out at different temperatures. Various bending strategies are studied. The findings point to the value for these materials in heating the bend during the forming operation to avoid cracking, in some cases, and to minimize springback. An analysis of the sheet metal distortion mechanism is carried out based on micrographic sections sampled in the bend. The analysis highlights the formation of “macro-bands” indicating the location of the distortion. Asperities are observed on the outer surface. This could be the fracturing site of certain grains located in the grooves of the asperities, with possible intergranular or transgranular cracking. A potential follow-up to this study could be to assess the changes in the mechanical characteristics after the aluminum alloy sheets have cooled to room temperature.
Cryogenic deep drawing of aluminum alloy AA6014 using macro-structured tools
Authors: Tulke M , Wolf A , Brosius A
Published: June 2021

For functional lightweight construction, 6xxx aluminum alloys are essential materials for exterior components due to their low weight to stiffness ratio and acceptable formability. The formability of the 6xxx alloys is lower compared to other aluminum alloys but they are free of flow lines. MOUSAVI ET AL. [1] demonstrate an alternative method of improving the forming limit with a deep drawing process using macro-structured tools. Another approach increasing the formability of aluminum alloys is forming at cryogenic temperatures [2]. This paper presents an advancement of deep drawing on macro-structured tools at cryogenic temperatures. This assumes a lower heat flux due to the reduction of the contact area between the blank and deep drawing tools, enabling forming at cryogenic blank temperature. After characterization of the material, experimental investigations are carried out on a cup test geometry. In addition to the required punch force at different temperatures, this paper presents the influence of macro-structured tools at cryogenic temperatures on springback and hardness distribution. Finally, the extension of the process limits and options by cryogenic macro-structured deep drawing are discussed.
Influence of synthetically generated inclusions on the stress accumulation and concentration in X65 pipeline steel
Authors: Fehlemann N. , Sparrer Y. , Pütz F. , Konemann M. , Münstermann S.
Published: June 2021

The use of a simulative approach with representative volume elements (RVE’s) is particularly well suited to investigate the influence of different microstructural parameters on the damage behavior of a material. In order to statistically analyze the individual components of the microstructure (e.g. geometric structure of grains and inclusions), well-known distribution functions such as logNormal/Gamma are normally used, but these do not take into account the interdependencies between the different parameters. However, newer approaches like machine learning techniques can only describe one phase of a single material at a time. Therefore, in this study, we extended an existing Wasserstein Generative Adversarial Network (WGAN) to a Conditional Wasserstein GAN with Gradient Penalty (CWGAN-GP), with which it is possible to process multiple materials/phases simultaneously. Training this algorithm on different steels and associated inclusions showed that a single trained network can generate synthetic microstructure for all different phases and materials with very high quality. A newly implemented evaluation method using the regularized Wasserstein-distance confirmed the excellent agreement of the real data with the synthetic data for all phases/materials. As a use case for our algorithm, the influence of different inclusions on the stress accumulation and concentration of X65 pipeline steel was investigated to find initiation sites for damage in the material. These investigations showed a pronounced correlation between stress concentration and inclusion parameters, thus confirming the usefulness of the CWGAN-GP as an input-generator for RVE’s.
Experimental research of formability limits in different thicknesses of polycarbonate sheets
Authors: Rosa-Sainz A , Magrinho JP , Silva M B , Centeno G , Martínez-Donaire A J , Vallellano C
Published: June 2021

This experimental investigation evaluates the methodologies for determining the forming limits by necking and fracture in polycarbonate (PC) sheets. The proposed approaches are based on two methodologies that are commonly utilized in sheet metal forming. To that end, Nakajima tests for polymer specimens with different strain loading paths were carried out for 1 mm, 2 mm and 3 mm thickness. The evaluation of the principal strains was accomplished by means of Digital Image Correlation (DIC) and thickness measurements to obtain failure strains were performed. The experimental results highlighted the different behaviour attained in polymers and metals, and the need of establishing a suitable adaptation of the methodologies used in sheet metal forming, especially due to the elastic recovery of polymers that cannot be neglected. This analysis allowed obtaining accurate formability limits by necking and by fracture for the PC sheets of 1, 2 and 3 mm of thickness, additionally these results were compared with the formability limits for PVC sheet of 3 mm of thickness. The representation of these formability limits within the principal strain space allowed establishing a general framework for analysing the fracture limit, which is the relevant forming limit in incremental sheet forming processes.
Influence of the strain dependent material behaviour under plane strain on the yield locus modelling
Authors: Lenzen M , Merklein M
Published: June 2021

Modern lightweight materials mostly exhibit a low formability especially in the plane strain state. Having in mind that over 80% of the occurred failures in the press shop in the automotive sector can be related to this strain state, the characterization under plane strain load should be further intensified. The evaluation of the plane strain flow curve is commonly done by notched tensile tests or biaxial tensile tests with optimized strain path. Both tests have some disadvantages in the flow curve evaluation especially at a high degree of deformation. With an elliptic hydraulic bulge test, the material behaviour under near plane strain condition can be evaluated up to fracture. The aim in this investigation is the analysis of the resulting material behaviour under plane strain of commonly used alloys AA5182, DC06 and DP600 with respect to the material anisotropy. Therefore, hydraulic bulge tests with a plane strain load path are performed in rolling direction and transversal direction. The resulting flow curves are used to analyse the material hardening with respect to the anisotropy. The results show differing hardening mechanisms for the investigated materials which will lead to different strategies for the material modelling.
Evaluation of Simple Shear Test Geometries for Constitutive Characterization using Virtual Experiments
Authors: Narayanan A , Abedini A , Weinschenk A , Worswick M J , Butcher C
Published: June 2021

In-plane simple shear tests have become commonplace in the fracture characterization of automotive sheet metals but have received less attention for constitutive characterization. Unlike tensile tests, simple shear tests do not have any tensile instability and remain in a state of plane stress until fracture. From plastic work equivalence, an isotropic hardening model can be readily constructed from the tensile and shear test data without inverse finite-element analysis. The success of the methodology hinges upon the shear specimen geometry and how the local strains in the gage region are measured using digital image correlation (DIC). In this study, finite-element simulations of seven shear test geometries were evaluated for an isotropic material in a series of virtual experiments by varying the input hardening response. The data from the simulations was extracted from the surface as if DIC was employed and used to determine the hardening behavior in comparison with the exact solution. Shear geometries without a notch eccentricity in the gage region appear to be best suited for characterizing low hardening materials with an error of less than 1% in the stress response for an n-value of 0.02. Conversely, for higher hardening materials corresponding to an n-value of 0.20 or greater, the geometries with a notch eccentricity performed best.
Modeling continuous dynamic recrystallization of lightweight alloys by coupling polycrystal plasticity approach
Authors: Chen S F , Zhang S H , Song H W , Lee M G
Published: June 2021

In the thermo-mechanical process of lightweight alloys, such as aluminum alloys, complex microstructure evolutions are inevitably involved via the continuous dynamic recrystallization (CDRX) featured with extensive formation of subgrains followed by progressive transition into new grains. In this study, a novel fully integrated CDRX-VPSC (visco-plastic self-consistent) model is established. First, numerical formulations for formation and rotation of subgrains are addressed by reasonably tackling the grain boundary characteristics, and also the concept of generation for CDRX grains is newly introduced. By considering these two aspects, the grain population is updated according to the complex grain boundary evolutions. In the VPSC module of the integrated modeling, the shear strain rate, dislocation density, and orientation are calculated to update the grain populations and grain sizes in the CDRX module. The validation of the proposed model is conducted by simulating the hot compression of extruded AA7075 sheet, in which the DRX mechanism is controlled by the subgrain related dynamic recovery (DRV) and CDRX. The simulated flow stresses, microstructural evolutions (grains size and DRX fractions), and texture features agree well with reported experimental observations.
Influence of the orthotropic behaviour on defects prediction in cup drawing, reverse redrawing and expansion
Authors: Oliveira M C , Neto D M , Alves J L , Menezes L F
Published: June 2021

Finite elements analysis is commonly used in the cans tool design since it allows predicting different sheet metal defects and instabilities that significantly affect the efficient production of beverage cans. These defects include earing, due to the material orthotropic behaviour, thinning and fracture. The numerical prediction of these kind of defects is more complex when different combinations of strain paths are involved. The process conditions considered in this work involve the drawing of a cylindrical cup, the reverse redrawing and the expansion. The two materials under analysis are an AA5352 aluminium alloy and a TH330 steel. The materials orthotropic plastic behaviour is modelled with a non-quadratic yield criterion. The results show that changes in the yield surface lead to slight changes in the earing profile and in the location were strain localization occurs. Moreover, the numerical model must describe in detail the process conditions, since they may affect the formability prediction.
Development of an automatic crack detection method for cupping tests on sheets and foils with a wall thickness below 0.1 mm
Authors: Schneider J-L , Staupendahl D , Wahlers L
Published: June 2021

In deep drawing and stretch forming, in-situ crack detection is usually performed by detecting the drop in drawing force, by analyzing structure-borne sound or by reflected light methods. Friction, vibration, and machine noise are disturbance variables that prevent crack detection in thin sheets and foils using the first two methods and highly reflective as well as inhomogeneous surfaces prevent crack detection in the last method. In order to avoid the above-mentioned disadvantages of the existing crack detection methods, a method based on transmission-illumination was developed. Key to this new development is the use of a translucent punch, which incorporates a light source, and a camera connected to an image-processing unit. The detection process works as follows: the luminous punch penetrates the sheet and forms it accordingly. As soon as a crack is formed, light penetrates the crack and falls onto the image sensor of the camera. The image processing unit detects the jump in illumination and triggers the sudden stop of the forming process. Forming tests were performed that show the stable and operator independent performance of the newly developed detection process using sheet samples made from steel and aluminum.
Deformation and thinning field prediction for HFQ® formed panel components using convolutional neural networks
Authors: Attar H R , Zhou H , Li N
Published: June 2021

The novel Hot Forming and cold die Quenching (HFQ®) process can provide cost-effective and complex deep drawn solutions through high strength aluminium alloys. However, the unfamiliarity of the new process prevents its widescale adoption in industrial settings, while accurate Finite Element (FE) simulations using the most advanced material models take place late in design processes and require forming process expertise. Machine learning technologies have recently been proven successful in learning complex system behaviour from representative examples and have the potential to be used as design support tools for new forming technologies such as HFQ®. This study, for the first time, presents a novel application of a Convolutional Neural Network (CNN) based surrogate to predict the deformation and thinning fields for variable deep drawn geometries formed using HFQ® technology. A dataset based on deep drawn geometries and corresponding FE results is generated and used to train the model. The results show that near indistinguishable full field predictions in real time are obtained from the surrogate when compared with HFQ® simulations. This technique can be adopted in industrial settings to aid in both concept and detailed component design for complex-shaped panel components formed under HFQ® conditions, without underlying knowledge of the forming process.
Prediction of forming limit diagrams from tensile tests of automotive grade steels by a machine learning approach
Authors: Finamor F P , Wolff M A , Lage V S
Published: June 2021

Steels’ formability is extremely important to the automotive industry. This property is usually assessed through the Forming Limit Diagrams (FLDs), which comprise the regions of maximum strains, where neither necking nor fracture of the material is observed. In this work, the use of Machine Learning algorithms was evaluated for the FLDs’ construction, based on the tensile properties of a group of steels. A set of historical data, consisting of tensile tests values and measured FLDs, based on Nakajima method of various AHSS, HSLA and IF steels, was used to build the model. In order to evaluate the predictive capacity of the model, experimental and Keeler-Brazier FLDs were compared. The proposed method was able to predict with great correlation and low mean error the FLDs of those materials. The results show a viable route for predicting FLDs based on tensile properties.
Autoencoder based Wear Assessment in Sheet Metal Forming
Authors: Niemietz Philipp , Unterberg Martin , Trauth Daniel , Bergs Thomas
Published: June 2021

The amount of information contained in process signals such as acoustic emission and force signals has proven vital for the detection of changes in physical conditions or quality feature prediction in sheet metal forming applications. Both signal types have also been researched in the context of wear detection, yet systems that reliably identify the wear state at a given time in sheet metal forming processes based on these signals do not exist. This paper proposes an architecture to assess the wear increase within a given time frame in an experiment based on an autoencoder. The ability of autoencoders to encode and decode signals has been widely studied and this approach leverages the fact that autoencoders are more likely to learn representative encodings on stable and homogeneous signals than on heterogeneous signals with high fluctuations. This approach utilizes the circumstance that high tool wear leads to changes in the signal and signal fluctuation. In consequence, autoencoders can be utilized to track tool wear progression without the need for labelled data. The findings show a strong similarity to physical models for the wear progression of tool components, indicating the validity of this approach. Additionally, an analysis of the signals yields characteristic effects of the considered force signals that could specifically represent wear resistance.
Load-specific variant generation of bead cross sections in sheet metal components by unidirectional carbon fibre reinforcement
Authors: Ott M , Haberkern P , Gruber M , Hartmann C , Risch T , Wunderling C , Albers A , Volk W
Published: June 2021

Beads are widely used to stiffen sheet metal components subjected to bending loads. Often, these bead-stiffened parts are used in product variants that differ significantly in the amount of acting loads. Lamination of unidirectional carbon fibre reinforced plastic (UD-CFRP) on the top flange area of individual beads represents a method for further increasing weight-specific stiffness: By varying the number of plies, a specifically configured component is obtained for each of the load cases. As a result, no changes to the forming tools are necessary and a minimum amount of the UD-CFRP material is required. In this work, a complete manufacturing process for a fibre reinforced bead was developed: First, a bead cross section geometry with an adapted top flange area to accommodate the UD-CFRP plies was designed and stamped into pre-stretched sheet samples of DX56 steel. Subsequently, the suitability of several surface pre-treatment processes to achieve sufficient bond strength of the composite bead was experimentally investigated and the UD-CFRP plies were applied by lamination. Final bending tests quantified the achievable stiffening effect of the investigated bead variants, showing a significant increase of the maximum supportable load compared to the standard non-reinforced cross-section.
Prediction and assessment of skid line formation during deep drawing of sheet metal components by using FEM simulation
Authors: Cyron P , Liewald M
Published: June 2021

The subjective perception of the quality of sheet metal components mainly depends on geometric characteristics and surface structures. In this context, particular attention must be paid to avoiding surface defects such as skid lines during the sheet metal forming process for components with high surface quality requirements (e.g. outer skin passenger car panels). In principal, FEM simulation can provide an effective tool for predicting such surface defects. However, the numerical modelling approaches available today do not yet allow an adequate basis for assessing their quality relevance in production, which especially applies to skid lines. In a previously published study, new skid line criteria were developed in this regard, considering unbending strain, thinning and major strain. Using a simple steel sheet part (DC06) as reference, the study showed that these criteria allow the quality relevance of skid lines to be predicted relatively accurately. This paper focuses on the validation of the proposed skid line criteria and their applicability to the materials DC06 and AA6016. Furthermore, the numerical studies presented show that one of the novel skid line criteria, which considers unbending strain and thinning, is able to accurately locate and predict the quality relevance of skid lines even for complex shaped parts.
Study on the self-propulsion of the rigid-flexible composite plate
Authors: Wu Wenbo
Published: June 2021

For both real fish and bionic fish, a rigid anterior portion is necessary for certain functions. How does the rigid anterior portion affect the locomotion of the flexible plate? Is it true that the rigid portion is redundant? It is lack of clear cognition on these questions. In this paper, the self-propulsion of the rigid-flexible composite plate is studied numerically. We suppose that the forces are exerted on the junction point to maintain a given pitch motion of the rigid portion, the deformation of the flexible portion is consequent. The ratio between the lengths of the flexible portion and the rigid portion is changed to model the composite plate, and the effect of the stiffness of the flexible plate is investigated. It is found that the propulsive velocity and the Froude efficiency actually decrease following the increasing proportion of the rigid plate. However, the conclusion is different as the elastic energy stored in the flexible plate is considered. We find that the case with larger flexible portion is efficient for the ultra-soft posterior plate, while the case with smaller flexible portion is efficient for the stiff posterior plate. It happens to coincide with the swimming behavior of live fish. The hydrodynamic force at the tail is hindering the propulsion of the plate, which means that the motion of the tail plays a decisive role on the force distribution on the plate, rather than the thrust only produced at the tail. We think that the short ultra-soft membrane at the tail of the real fish is an important feature to improve its swimming behavior. It is expected that the study in this paper will give a further insight into the mechanism of the locomotion of fish and give some implications for the design of the soft bionic fish.
One-step, low temperature synthesis of reduced graphene oxide decorated with ZnO nanocrystals using galvanized iron steel scrap
Authors: Tolentino-Hernandez R V , Jimenez-Melero E , Espinosa-Faller F J , Guarneros-Aguilar C , Caballero-Briones F
Published: June 2021

Production of a ZnO–rGO composite, using a novel one-pot method consisting in continuously flowing argon into a GO aqueous suspension heated at 80 °C, in the presence of galvanized iron steel scrap is presented. FTIR shows the complete disappearance of GO functional groups and only the C=C band remained, indicating extensive GO reduction. Raman spectra indicated sp2 character increase after reaction and the presence of the E2h mode of ZnO. SEM showed submicron crystals identified by XRD as ZnO in the hexagonal phase, while TEM images indicate ZnO nanoparticles decorate mainly the rGO borders. Optical band gap of 3.5 eV corresponding to ZnO, and optical transitions at 4.1 and 5.5 eV related with n → π and π → π* were observed. Electrochemical characterization by cyclic voltammetry shows an specific capacitance of 4.7 F g−1 at a scan rate of 5 mVs−1, which drops to ca. 0.8 F g−1 at 200 mVs−1. By electrochemical impedance spectroscopy, the relaxation time was ca. 5 ms. The proposed mechanism for the materials‘ synthesis includes Zn dissolution from scrap, galvanic displacement of oxygen moieties at the GO sheet, Zn deposition onto the carbon surface, and further oxidation and growth of ZnO nanocrystals.
The effect of temperature and ligand structure on the solubility of gold nanoparticles
Authors: Tarakame Samani Mandana , Hashemianzadeh Seyed Majid
Published: June 2021

In order to investigate the effect of ligands structure, and temperature on the solubility of the smallest crystallographic gold nanoparticle, Au18S14, quantum mechanical calculations, and molecular dynamics simulations have been performed. Ligands including 2-dimethyl amino Ethan thiol, 4-mercapto benzoic acid, and 3-mercapto-propionic acid have been used to study the effect of ligand type and temperature, and 4-mercapto butyric acid and 5-sulfanyl pentanoic acid ligands have been used in comparison to the 3-mercapto-propionic acid ligand to study the effect of carbon-chain length differences. Furthermore, three different temperatures: 290, 300, and 310 kelvin have been used to study the effect of temperature. The optimized structures of nanoparticles, electronic band-gap, light absorption, dipole moment values, and hardness were obtained using quantum mechanical methods. Further, hydrogen bond number, root mean squared displacement, the moment of inertia, radial distribution functions, mean square displacement, and solvent accessible surface area parameters were studied by molecular dynamic simulation methods. All quantum mechanics analyses indicated that functionalization improves the nanoparticle’s electronic features, solubility, and stability. The studies which have performed with the molecular dynamics simulations indicated that increasing the temperature leads to form more hydrogen bonds between gold nanoparticles and water, making them more soluble. Also, the structures with a longer carbon chain of ligands have stronger interactions with solvent but their mobility in the water can be decreased. From all data of this work, it can be concluded that the 4-mercapto benzoic acid is the ligand that makes more solubility and stability for the mentioned gold nanoparticle.
Near-infrared photodetection using random networks of single-walled carbon nanotubes with asymmetrical work-function electrodes
Authors: Sapankaew Mongkol , Dumnernpanich Weerapad , Jompol Yodchay
Published: June 2021

We investigate the use of random networks of single-walled carbon nanotubes for near-infrared photodetection. By increasing the number of nanotubes between asymmetrical work-function electrodes using dielectrophoretic assembly, the effect of Fermi-level pinning of nanotube-Schottky contacts was revealed in the linear current-voltage characteristic. The extracted device resistance showed an abrupt drop when the numerous intertube junctions formed densely packed networks in the electrode channel. Under the excitation of a near-infrared laser, we performed the photocurrent measurement at ambient temperature at different light powers. Our devices with densely packed nanotube networks showed enhanced photoconductive detection of responsivity, detectivity, and detection response. This is attributed to the increase in the photoabsorption area, the decrease of the channel resistance, and the formation of continuous conducting paths for high-efficient charge percolation. The photoconductive responsivity of up to 8.0 μA W−1 was found with a detectivity of about 4.9 × 105 cm Hz1/2 W−1, which is 4 orders of magnitude greater than that achieved in the channel with individual nanotubes deposited and comparable to that of suspended nanotube bolometers. The densely packed nanotube devices had a detection response of ∼ 4 ms under a finite bias that can be explained by the short-diffusion length of the photoexcited electrons and holes. However, the decrease in the photocurrent with time observed in our devices that exhibited photovoltaic characteristics indicates that electron-hole pair recombination in the nanotube networks occurs with differing characteristic time scales of the injected electrons and holes.
Measure and dimension of sums and products
Authors: Hambrook Kyle , Taylor Krystal
Published: June 2021

We investigate the Fourier dimension, Hausdorff dimension, and Lebesgue measure of sets of the form

R
Y
+
Z
,

RY + Z,

where

R
R

is a set of scalars and

Y
,
Z

Y, Z

are subsets of Euclidean space. Regarding the Fourier dimension, we prove that for each

α
∈
[
0
,
1
]

\alpha \in [0,1]

and for each non-empty compact set of scalars

R
⊆
(
0
,
∞
)

R \subseteq (0,\infty )

, there exists a compact set

Y
⊆
[
1
,
2
]

Y \subseteq [1,2]

such that
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="dimension Subscript upper F Baseline left-parenthesis upper Y right-parenthesis equals dimension Subscript upper H Baseline left-parenthesis upper Y right-parenthesis equals ModifyingAbove dimension Subscript upper M Baseline With bar left-parenthesis upper Y right-parenthesis equals alpha">

dim
F

⁡
(
Y
)
=

dim
H

⁡
(
Y
)
=

dim
M

¯

(
Y
)
=
α

\dim _F(Y) = \dim _H(Y) = \overline {\dim _M}(Y) = \alpha

and
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="dimension Subscript upper F Baseline left-parenthesis upper R upper Y right-parenthesis greater-than-or-equal-to min left-brace right-brace comma 1 comma plus plus of dimdimF left-parenthesis right-parenthesis upper R of dimdimF left-parenthesis right-parenthesis upper Y">

dim
F

⁡
(
R
Y
)
≥
min
{
1
,

dim
F

⁡
(
R
)
+

dim
F

⁡
(
Y
)
}

\dim _F(RY) \geq \min \{ 1, \dim _F(R) + \dim _F(Y)\}

. This theorem verifies a weak form of a more general conjecture, and it can be used to produce new Salem sets from old ones. Further, we investigate lower bounds on the measure and dimension of

R
Y
+
Z

RY+Z

for

R
⊂
(
0
,
∞
)

R\subset (0,\infty )

and arbitrary

Y
Y

and

Z
Z

; these latter results provide a generalized variant of some theorems of Wolff and Oberlin in which

Y
Y

is the unit sphere.
Appropriate deprescribing in older people: a challenging necessityCommentary to accompany themed collection on deprescribing
Authors: van der Velde Nathalie , Minhas Jatinder S
Published: June 2021

Older people are often taking several medications for a number of different medical conditions. Although physicians prescribe medications to treat diseases and symptoms, there may be also harmful side effects, especially so in older people taking several medications. Unfortunately, regular review of the benefits or risks of prescribed medications is as of yet not part of standard care. Also, data on how and in whom to stop medications in older people are scarce. The reason this is an important area of work is that medication related issues in older people are a common cause of harm, including both expected and unexpected effects of medications. Research to date tells us that to ensure successful implementation of structured and appropriate deprescribing, careful planning within hospital systems is needed. This includes involving different members of the team to ensure the patients truly benefit. The themed collection published on the Age and Ageing journal website offers key articles providing tools to assist decision-making, implementation strategies and multidisciplinary interventions—all with the aim of improving patient outcome and sustainability of deprescribing approaches.
Improved prediction of protein–protein interaction using a hybrid of functional-link Siamese neural network and gradient boosting machines
Authors: Mahapatra Satyajit , Sahu Sitanshu Sekhar
Published: June 2021

In this paper, for accurate prediction of protein–protein interaction (PPI), a novel hybrid classifier is developed by combining the functional-link Siamese neural network (FSNN) with the light gradient boosting machine (LGBM) classifier. The hybrid classifier (FSNN-LGBM) uses the fusion of features derived using pseudo amino acid composition and conjoint triad descriptors. The FSNN extracts the high-level abstraction features from the raw features and LGBM performs the PPI prediction task using these abstraction features. On performing 5-fold cross-validation experiments, the proposed hybrid classifier provides average accuracies of 98.70 and 98.38%, respectively, on the intraspecies PPI data sets of Saccharomyces cerevisiae and Helicobacter pylori. Similarly, the average accuracies for the interspecies PPI data sets of the Human-Bacillus and Human-Yersinia data sets are 98.52 and 97.40%, respectively. Compared with the existing methods, the hybrid classifier achieves higher prediction accuracy on the independent test sets and network data sets. The improved prediction performance obtained by the FSNN-LGBM makes it a flexible and effective PPI prediction model.
AdaTiSS: a novel data-Adaptive robust method for identifyingTissueSpecificityScores
Authors: Wang Meng , Jiang Lihua , Snyder Michael P
Published: June 2021

Motivation

Accurately detecting tissue specificity (TS) in genes helps researchers understand tissue functions at the molecular level. The Genotype-Tissue Expression project is one of the publicly available data resources, providing large-scale gene expressions across multiple tissue types. Multiple tissue comparisons and heterogeneous tissue expression make it challenging to accurately identify tissue specific gene expression. How to distinguish the inlier expression from the outlier expression becomes important to build the population level information and further quantify the TS. There still lacks a robust and data-adaptive TS method taking into account heterogeneities of the data.

Results

We found that the key to identify tissue specific gene expression is to properly define a concept of expression population. In a linear regression problem, we developed a novel data-adaptive robust estimation approach (AdaReg) based on density-power-weight under unknown outlier distribution and non-vanishing outlier proportion. The Gaussian-population mixture model was considered in the setting of identifying TS. We took into account heterogeneities of gene expression and applied the robust data-adaptive procedure to estimate the population parameters. With the well-estimated population parameters, we constructed the AdaTiSS algorithm.

Our AdaTiSS profiled TS for each gene and each tissue, which standardized the gene expression in terms of TS. We provided a new robust and powerful tool to the literature of defining TS.

Availability and implementation

https://github.com/mwgrassgreen/AdaTiSS.

Supplementary information

Supplementary data are available at Bioinformatics online.
Barrett’s oesophagus and oesophageal cancer following oesophageal atresia repair: a systematic review
Authors: Tullie L , Kelay A , Bethell G S , Major C , Hall N J
Published: June 2021

Background

Concern exists that patients born with oesophageal atresia (OA) may be at high risk for Barrett’s oesophagus (BO), a known malignant precursor to the development of oesophageal adenocarcinoma. Screening endoscopy has a role in early BO identification but is not universal in this population. This study aimed to determine prevalence of BO after OA repair surgery, to quantify the magnitude of this association and inform the need for screening and surveillance.

Methods

A systematic review, undertaken according to PRISMA guidelines, was preregistered on PROSPERO (CRD42017081001). PubMed and EMBASE were interrogated using a standardized search strategy on 31 July 2020. Included papers, published in English, reported either: one or more patients with either BO (gastric/intestinal metaplasia) or oesophageal cancer in patients born with OA; or long-term (greater than 2 years) follow-up after OA surgery with or without endoscopic screening or surveillance.

Results

Some 134 studies were identified, including 19 case reports or series and 115 single- or multi-centre cohort studies. There were 13 cases of oesophageal cancer (9 squamous cell carcinoma, 4 adenocarcinoma) with a mean age at diagnosis of 40.5 (range 20–47) years. From 6282 patients under long-term follow-up, 317 patients with BO were reported. Overall prevalence of BO was 5.0 (95 per cent c.i. 4.5 to 5.6) per cent, with a mean age at detection of 13.8 years (range 8 months to 56 years). Prevalence of BO in series reporting endoscopic screening or surveillance was 12.8 (95 per cent c.i. 11.3 to 14.5) per cent.

Conclusion

Despite a limited number of cancers, the prevalence of BO in patients born with OA is relatively high. While limited by the quality of available evidence, this review suggests endoscopic screening and surveillance may be warranted, but uncertainties remain over the design and effectiveness of any putative programme.