bluuebunny/crossref_metadata_2025 huggingface dataset:
High-performance flexible metal-on-silicon thermocouple
Authors: Assumpcao Daniel , Kumar Shailabh , Narasimhan Vinayak , Lee Jongho , Choo Hyuck
Published: September 2018

We have demonstrated metal-on-silicon thermocouples with a noticeably high Seebeck coefficient and an excellent temperature-sensing resolution. Fabrication of the thermocouples involved only simple photolithography and metal-liftoff procedures on a silicon substrate. The experimentally measured Seebeck coefficient of our thermocouple was 9.17 × 10−4 V/°K, which is 30 times larger than those reported for standard metal thin-film thermocouples and comparable to the values of alloy-based thin-film thermocouples that require sophisticated and costly fabrication processes. The temperature-voltage measurements between 20 to 80 °C were highly linear with a linearity coefficient of 1, and the experimentally demonstrated temperature-sensing resolution was 0.01 °K which could be further improved up to a theoretical limit of 0.00055 °K. Finally, we applied this approach to demonstrate a flexible metal-on-silicon thermocouple with enhanced thermal sensitivity. The outstanding performance of our thermocouple combined with an extremely thin profile, bending flexibility, and simple, highly-compatible fabrication will proliferate its use in diverse applications such as micro-/nanoscale biometrics, energy management, and nanoscale thermography.
A novel method for detection of camellia oil adulteration based on time-resolved emission fluorescence
Authors: Chen Hui , Chen Bin , Lu Daoli
Published: September 2018

In this study, time-resolved emission fluorescence (TRES) combined with chemometrics was developed and employed for adulteration analysis of camellia oil. TRES was first decomposed by parallel factors analysis (PARAFAC). Next, an artificial neural network (ANN) model was built for the adulteration analysis. A linear range of 5–50%, a limit of detection (LOD) of 3% and root mean square error of prediction (RMSEP) values lower than 3% were achieved. Compared with the steady-state measurement, easy access to the information from fluorophores of low concentration was shown to be an intrinsic advantage of the time-resolved measurement; this advantageous characteristic was helpful for optimizing adulteration analysis. It was demonstrated that TRES combined with chemometrics was a simple, rapid and non-intrusive method for adulteration analysis of vegetable oil.
Antibiotic treatment of rat dams affects bacterial colonization and causes decreased weight gain in pups
Authors: Tulstrup Monica Vera-Lise , Roager Henrik Munch , Thaarup Ida Clement , Frandsen Henrik Lauritz , Frøkiær Hanne , Licht Tine Rask , Bahl Martin Iain
Published: September 2018

Intergenerational transmission of bacteria during birth initiates the natural successional development of the intestinal microbiota in mammals. This process can be disrupted by antibiotic exposure, potentially affecting early-life microbiota-dependent metabolic programming. In the present study, we specifically investigate the metabolic consequences of exposing neonate Wistar rats to an antibiotic-perturbed low-diversity microbiota from birth until weaning, without exposing the pups directly to antibiotics. Here, we show that pups born from both amoxicillin and vancomycin-treated dams gain less weight than controls. This was concordant with lower feed intake as well as increased colonic expression of the PYY satiety hormone gene at weaning. The weight difference persists into adulthood even though the initial differences in gut microbiota subsided. Our results demonstrate that early-life exposure to an antibiotic-perturbed low-diversity microbiota is sufficient to cause changes in body weight persisting into adulthood.
Carbon-based Nanomaterials in Analytical Chemistry
Authors: Crevillen Agustín G. , Escarpa Alberto , García Carlos D.
Published: September 2018

Carbon-based nanomaterials are amazing technological tools with unique properties (high mechanical strength, high conductivity, attractive optical properties, chemical versatility, etc.). Among them, graphene and carbon nanotubes are probably the most commonly used materials in chemical analysis. These carbon nanomaterials can be synthesized by several methods, which can be roughly classified in top-down and bottom-up methods. Their physicochemical characterization is essential to assure the product quality (purity, defects, chemical species on the surface, etc.) and to elucidate their structure. In this sense, Raman spectroscopy, electron microscopy and atomic force microscopy are the most important techniques. Moreover, the synthetic and purification route determines some properties of these materials so they must be carefully selected prior to their application. Without any doubt, graphene and carbon nanotubes have played an important role in chemical analysis (sample preparation, separation and detection) and the graphene derivatives “graphene nanoribbon” and “graphene quantum dots” will do the same. Therefore, it is expected that their routine use will be consolidated in the next few years.
Carbon Nanomaterials in Sample Preparation
Authors: Socas-Rodríguez B. , González-Sálamo J. , Hernández-Borges J.
Published: September 2018

Nanoscience and nanotechnology, which refer to the design, building, manipulation, and understanding of materials and systems at the nanoscale (sizes ranging from approximately 1 nm to 100 nm, in general) are currently at an extremely high level of development. Proof of this is that nanomaterials have found a very important place in a wide variety of areas, including analytical chemistry and, in particular, sample preparation procedures, as a result of their high porosity, high surface-to-volume ratio and ability to establish different types of interactions. Among them, carbon-based nanomaterials alone (i.e. carbon nanotubes, fullerenes, graphene, carbon nanohorns and nanodiamonds) or combined with others, have been successfully used as extraction or clean-up sorbents under different modes, which has widely expanded their application range. This chapter is aimed at providing a general overview of the different sample pre-treatments in which carbon-based nanomaterials have been applied, with special emphasis on the most recent applications.
A label-free and ultrasensitive electrochemical aptasensor for lead(ii) using a N,P dual-doped carbon dot–chitosan composite as a signal-enhancing platform and thionine as a signaling molecule
Authors: Xiao Qi , Feng Jinrong , Li Jiawen , Feng Mengmeng , Huang Shan
Published: September 2018

A label-free and ultrasensitive electrochemical aptasensor for lead(ii) using a N,P-CD–CS composite as a signal-enhancing platform and THi as a signaling molecule.
Isothermal control of probe–target interactions using graphene oxide and a nuclease for highly sensitive and specific detection of target DNA
Authors: Kim Joong Hyun , Chung Chan Ho
Published: September 2018

Isothermal control of target–probe interaction using graphene oxide and RNase H allows highly sensitive and specific detection of target DNA.
The effect of core–shell engineering on the energy product of magnetic nanometals
Authors: Zhang Wei , Yang Weibing , Chandrasena Ravini U. , Özdöl V. Burak , Ciston Jim , Kornecki Michael , Raju SelvaVennila , Brennan Raymond , Gray Alexander X. , Ren Shenqiang
Published: September 2018

The spin canting effect in FePt–FeCo (core–shell) nanostructures enhances the magnetic energy product.
Choline-mediated synthesis of zeolite ERS-7 via an excess fluoride approach
Authors: Bae Juna , Hong Suk Bong
Published: September 2018

A high-silica (Si/Al = 14) version of zeolite ERS-7 has been synthesized using choline ions under excess fluoride conditions.
Intrinsic structure of pentapeptide Leu-enkephalin: geometry optimization and validation by comparison of VSCF-PT2 calculations with cold ion spectroscopy
Authors: Roy Tapta Kanchan , Kopysov Vladimir , Pereverzev Aleksandr , Šebek Jiří , Gerber R. Benny , Boyarkin Oleg V.
Published: September 2018

Intrinsic structure of pentapeptide Leu-enkephalin: quantum VSCF calculations meet cold ion spectroscopy.
The prediction of far-infrared spectra for planetary nitrile ices using periodic density functional theory with comparison to thin film experiments
Authors: Ennis C. , Auchettl R. , Appadoo D. R. T. , Robertson E. G.
Published: September 2018

The application of high accuracy periodic DFT calculations to replicate laboratory thin film spectra allowing the assignment of vibrational far-infrared modes in nitrile-bearing planetary ices.
Superconductivity and phase stability of potassium-doped biphenyl
Authors: Zhong Guo-Hua , Yang Dong-Yu , Zhang Kai , Wang Ren-Shu , Zhang Chao , Lin Hai-Qing , Chen Xiao-Jia
Published: September 2018

The Meissner effect is observed in potassium-doped biphenyl and the crystal structure is predicted.
Fe-doped γ-Al2O3 porous hollow microspheres for enhanced oxidative desulfurization: facile fabrication and reaction mechanism
Authors: Zhao Wentao , Zheng Xiaohai , Liang Shijing , Zheng Xiaoxiao , Shen Lijuan , Liu Fujian , Cao Yanning , Wei Zheng , Jiang Lilong
Published: September 2018

Fe-Doped γ-Al2O3 porous hollow microspheres with hierarchical porosity were fabricated as efficient catalysts for H2S selective oxidation.
Combination of support vector regression (SVR) and microwave plasma atomic emission spectrometry (MWP-AES) for quantitative elemental analysis in solid samples using the continuous direct solid sampling (CDSS) technique
Authors: Niu Guanghui , Shi Qi , Yuan Xin , Wang Jie , Wang Xu , Duan Yixiang
Published: September 2018

Direct elemental analysis in solid samples was achieved using the continuous direct solid sampling (CDSS) technique based on microwave plasma.
Structural optimization and antibacterial evaluation of rhodomyrtosone B analogues against MRSA strains
Authors: Zhao Liyun , Liu Hongxin , Huo Luqiong , Wang Miaomiao , Yang Bao , Zhang Weimin , Xu Zhifang , Tan Haibo , Qiu Sheng-Xiang
Published: September 2018

Methicillin-resistant Staphylococcus aureus (MRSA) infections are well-known as a significant global health challenge.
Spatially resolved solid-state reduction of graphene oxide thin films
Authors: Morant-Miñana Maria C. , Heidler Jonas , Glasser Gunnar , Lu Hao , Berger Rüdiger , Gil-Gonzalez Nerea , Müllen Klaus , de Leeuw Dago M. , Asadi Kamal
Published: September 2018

Controlled reduction of GO thin-films at room temperature with spatial resolution simply by application of a voltage, without the intentional use of electrolytes, has been demonstrated.
Polarization-dependent surface plasmon-driven catalytic reaction on a single nanowire monitored by SERS
Authors: Li Ze , Gao Yanan , Zhang Lisheng , Fang Yan , Wang Peijie
Published: September 2018

The polarizing effect of an excitation laser on a plasmon-driven catalytic reaction on a single nanowire (NW) was investigated experimentally and theoretically.
Achieving high-performance nitrate electrocatalysis with PdCu nanoparticles confined in nitrogen-doped carbon coralline
Authors: Chen Miao , Wang Haifeng , Zhao Yuye , Luo Wei , Li Li , Bian Zhenfeng , Wang Lianjun , Jiang Wan , Yang Jianping
Published: September 2018

Nitrogen-doped coral-like porous carbon embedded with small alloy nanoparticles was synthesized by a direct surfactant co-assembly approach and demonstrated excellent nitrate electrocatalysis ability.
The importance of N-heterocyclic carbene basicity in organocatalysis
Authors: Wang Ning , Xu Jiahui , Lee Jeehiun K.
Published: September 2018

This review highlights the importance of N-heterocyclic carbene (NHC) basicity for transformations in which NHCs are used as catalysts.
A star-shaped conjugated molecule featuring a triazole core and diketopyrrolopyrrole branches is an efficient electron-selective interlayer for inverted polymer solar cells
Authors: Chen Wei-Jen , Cheng Yu-Che , Kuo Da-Wei , Chen Chin-Ti , Liu Bo-Tau , Jeng Ru-Jong , Lee Rong-Ho
Published: September 2018

A novel triazole-cored, star-shaped, conjugated molecule (TDGTPA) has been synthesized for use as an electron-selective interlayer in inverted polymer solar cells (PSCs).
Designing an efficient graphene quantum dot-filled luminescent down shifting layer to improve the stability and efficiency of perovskite solar cells by simple optical modeling
Authors: Hosseini Zahra , Ghanbari Teymoor
Published: September 2018

Optical modeling of a GQD-filled LDS layer on top of a perovskite solar cell (PSC) confirms GQDs as a suitable candidate as a luminescent material for application of the LDS strategy in PSCs.
Recent progress in nanostructured transition metal nitrides for advanced electrochemical energy storage
Authors: Gao Biao , Li Xingxing , Ding Kang , Huang Chao , Li Qingwei , Chu Paul K. , Huo Kaifu
Published: September 2018

Recent advances and future opportunities pertaining to transition metal nitride based hybrid nanostructures for advanced electrochemical energy storage are reviewed.
Correlation‐guided multi‐object tracking with correlation feature transfer
Authors: Li Jiatong , Zhao Yanjie , Jiang Zhiguo
Published: September 2018

Here, the authors propose a correlation‐guided Monte Carlo Markov chain (MCMC) solver to promote the efficiency for tracking multiple objects under recursive Bayesian filtering framework. Instead of randomly proposing the target location according to certain distribution, the authors’ method guides the MCMC solver to sample among locations that the targets are more likely to appear. The high possible locations for each target are obtained using its corresponding response map by evaluating the correlation between the target appearance and its online model. Furthermore, the proposed tracking framework is natural to transfer the rich domain‐specific offline correlation features into the target online model. With the calculation in the Fourier domain and the reversible jump strategy for MCMC, the correlation‐guided method is able to track variable multiple objects with high efficiency. At the same time, the correlation feature transfer strategy is capable of improving tracking precision with easy offline training. The proposed method is evaluated by both the synthetic and real scenario videos. The experimental results demonstrate the effectiveness of the proposed method and its superior performance against its counterparts.
Edge gradient feature and long distance dependency for image semantic segmentation
Authors: Zhou Hao , Han Anqi , Yang Haodong , Zhang Jun
Published: September 2018

Image semantic segmentation is a challenging problem for low‐level computer vision. Recently, deep convolutional neural networks (DCNNs) have been proved to achieve outstanding performance in image semantic segmentation. Most current methods still have some problems in segmenting the object edges and the integrity of objects. In this study, the authors first construct the difference‐pooling module in the DCNNs to extract the object edge gradients and get finer boundary in segmentation results. Then the combination of the pyramid pooling module and the atrous spatial pyramid pooling extracts the image global features and the context structure information by building long‐distance dependency between pixels, which is just like a simple fully connected conditional random field (CRF). Different from other methods, the proposed method does not need extra pre‐processing and post‐processing steps, such as extracting gradient features by the traditional algorithm and building context relationships by CRF. Finally, the experimental results on the PASCAL VOC2012 benchmark indicate that the proposed model can obtain the finer boundaries and more complete parts.
Approach to 3D face reconstruction through local deep feature alignment
Authors: Zhang Jian , Zhu Chaoyang
Published: September 2018

Here, the authors propose an end‐to‐end method based on deep learning to reconstruct three‐dimensional (3D) face models from given face images. In the training stage, the authors propose to extract the feature representations from the 3D sample faces and corresponding 2D sample images through the proposed local deep feature alignment (LDFA) algorithm, and estimate an explicit mapping from the 2D features to their 3D counterparts for each local neighbourhood, then the authors learn a feed‐forward deep neural network for each neighbourhood whose parameters are initialised with the parameters obtained in the locality‐aware learning process and the explicit mapping. In the testing stage, the authors only need to feed a given face image to the deep neural network corresponding to the nearest sample image and receive the outputted 3D face model. Extensive experiments have been conducted on both non‐face and face data sets. The authors find that the LDFA algorithm performs better than several popular unsupervised feature extraction algorithms, and the 3D reconstruction results obtained by the proposed method also outperform the comparison methods.
ANTIC: antithetic isomeric cluster patterns for medical image retrieval and change detection
Authors: Mandal Murari , Chaudhary Mallika , Vipparthi Santosh Kumar , Murala Subrahmanyam , Gonde Anil Balaji , Nagar Shyam Krishna
Published: September 2018

In this study, new feature descriptors are designed for medical image retrieval and change detection applications, respectively. Inspired by isomerism, the authors propose a novel feature descriptor named antithetic isomeric cluster pattern (ANTIC). The ANTIC is defined by the two properties: cluster patterns and antithetic isomerism (ANTI). The cluster pattern corresponds to successive pixel intensity differences at antithetical orientations. Furthermore, the ANTI is characterised by two aspects: first, the clusters are oppositely oriented (antithetical) to each other and second, both adhere to a defined isomeric property. The ANTIC identifies the lines and corner point information in the local neighbourhood across various directions. To attain enhanced robustness, they further proposed multiresolution ANTIC by integrating the multiresolution Gaussian filter. Moreover, to reduce the feature dimensionality, they extended their work to rotation invariant features. The proposed method outperforms other widely used feature descriptors in biomedical and retinopathy image retrieval applications. In addition, they extracted spatiotemporal features by designing intra‐ANTIC and inter‐ANTIC to detect motion changes in video sequences. They validated the effectiveness of these features by conducting experiments on CDNet 2014 dataset. The proposed descriptor achieves better performance in various challenging conditions for change detection as compared to other state‐of‐the‐art techniques.
High‐energy storage and temperature stable dielectrics properties of lead‐free BiScO3 –BaTiO3 –x (Bi0.5 Na0.5)TiO3 ceramics
Authors: Xie Hang , Liu Guobao , Yang Ling , Xu Jiwen , Zhou Changrong , Zhang Haibo , Yuan Changlai , Chen Guohua , Qiu Wei , Wang Hua
Published: September 2018

Lead‐free (1–x)(0.4BiScO3 –0.6BaTiO3)‐x (Bi0.5 Na0.5)TiO3 (BSBT–x BNT) ceramics were prepared by traditional ceramics preparation method. The energy storage characteristics, as well as dielectric spectrum curves of BSBT–x BNT ceramics, were systematically used in research. The ternary system formed perovskite solid solution with dense and homogenous microstructure. BSBT–x BNT ceramics exhibited slimmer and slanted hysteresis loops followed by higher saturation polarisation (P max) and lower remnant polarisation (P r), which induced high‐energy storage density of 1.39 J/cm3 (E  = 180 kV/cm). Ranging from 200 to 400°C, BSBT–x BNT ceramics had high permittivities, and a matching dielectric loss, which exhibited flat temperature coefficients of permittivity (TCɛ). The impedance spectroscopy analysis indicated that the non‐Debye relaxation mechanism existed in BSBT–x BNT ceramics. BSBT–x BNT ceramics may have potential application value for the high‐temperature capacitor.
Observational evidence in favor of scale-free evolution of sunspot groups
Authors: Shapoval A. , Le Mouël J.-L. , Shnirman M. , Courtillot V.
Published: September 2018

Context.The hypothesis stating that the distribution of sunspot groups versus their size (φ) follows a power law in the domain of small groups was recently highlighted but rejected in favor of a Weibull distribution.

Aims. In this paper we reconsider this question, and are led to the opposite conclusion.

Methods.We have suggested a new definition of group size, namely the spatio-temporal “volume” (V) obtained as the sum of the observed daily areas instead of a single area associated with each group.

Results.With this new definition of “size”, the width of the power-law part of the distributionφ∼ 1/Vβincreases from 1.5 to 2.5 orders of magnitude. The exponentβis close to 1. The width of the power-law part and its exponent are stable with respect to the different catalogs and computational procedures used to reduce errors in the data. The observed distribution is not fit adequately by a Weibull distribution.

Conclusions.The existence of a wide 1/Vpart of the distributionφsuggests that self-organized criticality underlies the generation and evolution of sunspot groups and that the mechanism responsible for it is scale-free over a large range of sizes.
Focusing on the extended X-ray emission in 3C 459 with a Chandra follow-up observation
Authors: Maselli A. , Kraft R. P. , Massaro F. , Hardcastle M. J.
Published: September 2018

Aims. We investigated the X-ray emission properties of the powerful radio galaxy 3C 459 revealed by a recent Chandra follow-up observation carried out in October 2014 with a 62 ks exposure.

Methods. We performed an X-ray spectral analysis from a few selected regions on an image obtained from this observation and also compared the X-ray image with a 4.9 GHz VLA radio map available in the literature.

Results. The dominant contribution comes from the radio core but significant X-ray emission is detected at larger angular separations from it, surrounding both radio jets and lobes. According to a scenario in which the extended X-ray emission is due to a plasma collisionally heated by jet-driven shocks and not magnetically dominated, we estimated its temperature to be ∼0.8 keV. This hot gas cocoon could be responsible for the radio depolarization observed in 3C 459, as recently proposed also for 3C 171 and 3C 305. On the other hand, our spectral analysis and the presence of an oxygen K edge, blueshifted at 1.23 keV, cannot exclude the possibility that the X-ray radiation originating from the inner regions of the radio galaxy could be intercepted by some outflow of absorbing material intervening along the line of sight, as already found in some BAL quasars.
Confirmation of double peaked Lyα emission at z = 6.593
Authors: Matthee Jorryt , Sobral David , Gronke Max , Paulino-Afonso Ana , Stefanon Mauro , Röttgering Huub
Published: September 2018

Distant luminous Lyman-α emitters (LAEs) are excellent targets for spectroscopic observations of galaxies in the epoch of reionisation (EoR). We present deep high-resolution (R = 5000) VLT/X-shooter observations, along with an extensive collection of photometric data of COLA1, a proposed double peaked LAE at z = 6.6. We rule out the possibility that COLA1’s emission line is an [OII] doublet at z = 1.475 on the basis of i) the asymmetric red line-profile and flux ratio of the peaks (blue/red=0.31 ± 0.03) and ii) an unphysical [OII]/Hα ratio ([OII]/Hα >  22). We show that COLA1’s observed B-band flux is explained by a faint extended foreground LAE, for which we detect Lyα and [OIII] at z = 2.142. We thus conclude that COLA1 is a real double-peaked LAE at z = 6.593, the first discovered at z >  6. COLA1 is UV luminous (M1500 = −21.6 ± 0.3), has a high equivalent width (EW0,Lyα = 120−40+50 Å) and very compact Lyα emission (r50,Lyα = 0.33−0.04+0.07 kpc). Relatively weak inferred Hβ+[OIII] line-emission from Spitzer/IRAC indicates an extremely low metallicity of Z <  1/20 Z⊙ or reduced strength of nebular lines due to high escape of ionising photons. The small Lyα peak separation of 220 ± 20 km s−1 implies a low HI column density and an ionising photon escape fraction of ≈15 − 30%, providing the first direct evidence that such galaxies contribute actively to the reionisation of the Universe at z >  6. Based on simple estimates, we find that COLA1 could have provided just enough photons to reionise its own ≈0.3 pMpc (2.3 cMpc) bubble, allowing the blue Lyα line to be observed. However, we also discuss alternative scenarios explaining the detected double peaked nature of COLA1. Our results show that future high-resolution observations of statistical samples of double peaked LAEs at z >  5 are a promising probe of the occurrence of ionised regions around galaxies in the EoR.
The X-ray/UV ratio in active galactic nuclei: dispersion and variability
Authors: Chiaraluce E. , Vagnetti F. , Tombesi F. , Paolillo M.
Published: September 2018

Context. The well established negative correlation between the αOX spectral slope and the optical/ultraviolet (UV) luminosity, a by-product of the relation between X-rays and optical/UV luminosity, is affected by relatively large dispersion. The main contributors to this dispersion can be variability in the X-ray/UV ratio and/or changes in fundamental physical parameters.

Aims. We want to quantify the contribution from variability within single sources (intra-source dispersion) and that from variations of other quantities different from source to source (inter-source dispersion).

Methods. We use archival data from the XMM-Newton Serendipitous Source Catalog (XMMSSC) and from the XMM-OM Serendipitous Ultraviolet Source Survey (XMMOM-SUSS3). We select a sub-sample in order to decrease the dispersion of the relation due to the presence of radio-loud and broad absorption line objects, and that due to absorptions in both X-ray and optical/UV bands. We use the structure function (SF) to estimate the contribution from variability to the dispersion. We analyse the dependence of the residuals of the relation on various physical parameters in order to characterise the inter-source dispersion.

Results. We find a total dispersion of σ ∼ 0.12 and find that intrinsic variability contributes 56% of the variance of the αOX − LUV relation. If we select only sources with a larger number of observational epochs (≥3) the dispersion of the relation decreases by approximately 15%. We find weak but significant dependencies of the residuals of the relation on black-hole mass and on Eddington ratio, which are also confirmed by a multivariate regression analysis of αOX as a function of UV luminosity and black-hole mass and/or Eddington ratio. We find a weak positive correlation of both the αOX index and the residuals of the αOX − LUV relation with inclination indicators, such as the full width at half maximum (Hβ) and the equivalent width (EW)[OIII], suggesting a weak increase of X-ray/UV ratio with the viewing angle. This suggests the development of new viewing angle indicators possibly applicable at higher redshifts. Moreover, our results suggest the possibility of selecting a sample of objects, based on their viewing angle and/or black-hole mass and Eddington ratio, for which the αOX − LUV relation is as tight as possible, in light of the use of the optical/UV – X-ray luminosity relation to build a distance modulus (DM)-z plane and estimate cosmological parameters.
Experimental and Numerical Studies on the Dynamic Behaviors of Concrete Material Based on the Waveform Features in SHPB Test
Authors: Weintu Chen Xiao , Lv Taihong , Chen Gang
Published: September 2018

The tendency of the waveform curve can directly reflect the deformation and failure process of specimen in the SHPB (Split Hopkinson Pressure Bar) test of concrete. Different loading rates will result in the different ultimate failure modes, waveform curves. Furthermore, these differences are obviously characterized by some feature points of waveform or stress-strain curves. It is to say for concrete-like damage softening materials, the waveform features contains lots of information of material response. In this study, large dimension (Ф120mm) SHPB tests of concrete specimens have been conducted. Four typical failure patterns of concrete specimens are classified, as well as some typical waveform features, e.g. the “double-peak” and“compression wave” phenomena of reflection wave, etc. On the other hand, the numerical simulations corresponding to the experimental tests are performed by means of the 3D meso-scale model of concrete material. In the numerical results, waveform features observed in experiment are reliably reproduced and predicted. Associating with waveform features, the violation indicator of the specimen stress equilibrium in the SHPB test is first identified for concrete-like damage softening materials. The concrete material behaviors forstress non-equilibrium are further analyzed, e.g. DIF and damage development, etc.
Bird strike on aircraft radome: Dynamic characterisation of quartz fibre composite sandwich for accurate, predictive impact simulations
Authors: Heimbs Sebastian , Wagner Tim , Meister Heinz , Brand Clemens , Calomfirescu Mircea
Published: September 2018

This study assesses the bird strike resistance of the satellite communication (SatCom) radome of a medium altitude, long endurance (MALE) remotely piloted aircraft system (RPAS), which is designed as a lightweight sandwich structure with thin quartz fibre composite skins and a cellular honeycomb core. In order to perform accurate, predictive numerical bird strike simulations, the building block approach was applied, involving extensive experimental characterisation and model validation of the materials and structures from simple coupon level up to full-scale radome level. Coupon tests of the quartz fibre composite skin material under high-rate dynamic loading revealed significant strain rate effects, which needed to be taken into account in the simulation model in order to predict the structural response under high-velocity bird strike loading. In summary, this work presents a systematic and detailed approach for obtaining validated modelling methods for high-velocity impact analyses, which could be used efficiently for various design and parameter studies during the development of the SatCom radome.
Experimental analysis and modelling of the strain-rate sensitivity of sheet niobium
Authors: Peroni Lorenzo , Scapin Martina
Published: September 2018

The niobium is currently used for the construction of the superconducting radio frequency (RF) Crab Cavity for the particle accelerator LHC at CERN in Geneva. An alternative technique to traditional forming methods is the electrohydraulic forming (EHF), in which ultrahigh-speed deformation of blank sheets is performed by using shockwaves electrically induced in water. A big effort is made for the analysis of the forming processes by FEM simulations, which require the definition of an appropriate flow stress material model. With this aim, in the present work, a testing campaign was performed in tension on sheet specimens with a rectangular cross-section at different strain-rates, up to 103 s-1. The obtained results showed the material is strongly sensitive to strain-rate, as expected for a pure BCC metal. The data, were processed via a reverse engineering procedure, based on finite element simulations of the experimental tests. This methodology allowed the identification of a tabular flow stress model (MAT_224 implemented in LSDYNA) for the prediction of the material behaviour as a function of the plastic strain, strain-rate and temperature.
Dynamic Resistance of Multi-Layered Protective Elements Under Impact Loads
Authors: Kruszka Leopold , Vorobiov Iurii , Ovcharova Nataliia
Published: September 2018

To ensure the dynamic strength of modern constructions, protective elements are used. Studies have shown that even with the use of double-layer elements from similar materials, multilayer elements have enhanced protective properties with a smaller overall thickness compared to single-layer elements. Even greater effect is achieved when using layers of different materials. These features are widely used in the creation of linings to strengthen the bodies of gas turbine engines when exposed to fragments of blades and foreign objects. Numerical studies of the stress-strain state of three-layer element from two thin layers of a titanium alloy and an average ceramic layer under the influence of projectile with different velocities are carried out. The top layer of the titanium alloy perceives the main local load and plastic deformations occur up to the formation of the crater. In the average ceramic layer, the extensive deformations develop, during which the basic energy of impact is absorbed. The third layer limits the velocity of deformation and increases the protective properties of the element. Thus, it is shown that the multilayer elements can have improved protective properties with a general reduction of the weight of structure.
High strain rate and high temperature response of two armour steels: Experimental testing and constitutive modelling
Authors: McDonald Brodie , Bornstein Huon , Ameri Ali , Escobedo-Diaz Juan P. , Orifici Adrian C.
Published: September 2018

Under ballistic impact or blast loading, the high strain rate and high temperature behaviour of armour steels is key to their response to a given threat. This experimental and numerical investigation examines the tensile response of a class 4a improved rolled homogenous armour steel (IRHA) and a high hardness armour steel (HHA). Cylindrical tensile specimens were tested at a range of strain rates from 0.001 s-1 to 2700 s-1. Quasi-static, elevated temperature tests were performed from room temperature up to 300° C. While the HHA is strain rate insensitive, the IRHA displays a significant increase in strength across the range of loading rates reducing the ultimate strength difference between the materials from 19% at 0.001s-1 to 4.6% at 2700s-1. An inverse numerical modelling approach for constitutive model calibration is presented, which accurately captured the dynamic material behaviour. The modified Johnson-Cook strength and Cockcroft-Latham (C-L) fracture models were capable of predicting the ballistic limit of each material to within 5% of the experimental result and to within 10% for deformation under blast loading. The blast rupture threshold of both materials was significantly over-estimated by the C-L model suggesting stress state or strain rate effects may be reducing the ductility of armour steel under localised blast loading.
Creation of database for strength calculation of constructions
Authors: Bragov Anatoly , Isaev Sergey , Kapustin Sergey , Konstantinov Alexander , Lomunov Andrey
Published: September 2018

The problems of creation of an automated system for obtaining, processing and storing experimental information on the physical and mechanical properties of structural materials, building materials and various soil media used to provide information support for automated computing systems for analysis of strength and design of structures are discussed. The developed database is focused on studying the effects of the behavior of structural materials under highly parametric influences of force, temperature and other physical fields, as well as on equipping and experimental substantiation of mathematical models describing these effects. In the proposed variant, the database is implemented as a client-server application executed on the Microsoft.Net Framework using a powerful database management system MS SQL Server. The content of the created bank is made up of sections of primary information, material properties and material models. In order to automate the processing of data at all stages of information conversion, a special “Desktop” subsystem is included in the bank, which allows aggregating data obtained from several different experiments, correcting the selected data, processing and converting it. Processing and transformation of data in the subsystem “Desktop” can be carried out either in manual mode or on the basis of special algorithms using appropriate mathematical methods.
Laser-induced cratering of a 3DCC material at mesoscale: Experiments and simulations
Authors: Jaulin Vincent , Hébert David , Aubert Bertrand , Rullier Jean-Luc , Malaise Frédéric , Lescoute Emilien
Published: September 2018

This study concerns the damaging of a 3-Dimension Carbon/Carbon (3DCC) composite material under dynamic loading. Experiments were performed with a laser facility delivering energies between 13 and 40 J with 100 nanoseconds pulse duration. The focal spot diameter was 250 μm, leading to dynamic pressure up to 10 GPa. The focal spot being smaller than the size of the composite components, it allows us to study the dynamic behaviour of the material at mesoscopic scale. The dynamic process of this cratering is then investigated via 3D numerical simulations, and a Johnson-Holmquist model is proposed. It appears that comparison of simulations with experimental results is useful to identify the dynamic strength of individual components of composite materials.
Study of wave propagation in poroviscoelastic halfspace under normal harmonic load via BEM
Authors: Ipatov Aleksandr , Litvinchuk Svetlana
Published: September 2018

The present research is dedicated to a problem of a soil dynamics in case when media is subjected to a normal harmonic load. Such type of load may be observed for example because of working wind generator, and the aim is to create a model of possible impact. One of the most appropriate ways for soil modelling is the Biot model of poroelastic media and its enhancements. In this paper we treat a soil as a poroviscoelastic media. Our poroviscoelastic formulation is based on Biot theory of poroelasticity and correspondence principle applied to skeleton of porous material. Standard linear solid model is employed to describe viscoelastic media properties. Boundary integral equations method is applied to solving threedimensional boundary-value problems. The solution of the original problem is constructed in Laplace transforms, with the subsequent application of the algorithm for numerical inversion. To introduce BEdiscretization, we consider the regularized boundary-integral equation. Mixed boundary element discretization is introduced to obtain discrete analogues. Modified Durbin’s algorithm of numerical inversion of Laplace transform is used. Research is also dedicated to development of numerical modeling technique based on Boundary Element Method (BEM) in Laplace domain of solution three dimensional poroviscodynamic problems. Numerical example of a poroviscoelastic halfspace under harmonic load is considered. Viscoelastic model parameter influence on dynamic responses of boundary functions is studied. The comparison of transient responses is presented.
Modelling and characterisation of the high-rate behaviour of rock material
Authors: Larsson Simon , Nishida Masahiro , Kurano Shuhei , Moroe Tomoki , Gustafsson Gustaf , Häggblad Hans-Åke , Jonsén Pär
Published: September 2018

For future reliable numerical simulations of impact wear on steel structures caused by rock material, knowledge about the dynamic mechanical properties of rock material is required. This paper describes the experimental and numerical work to investigate the dynamic mechanical properties of diabase (dolerite), a subvolcanic rock material. In this study, diabase from southern Sweden was used. The impact compressive strength of diabase with a density of 2.63 g/cm3 was examined by using the split-Hopkinson pressure bar (Kolsky bar) method. Cylindrical specimens were used, with a diameter of 8.9 mm and a length of 14 mm. To characterise the rock material, uniaxial compression tests were performed, at high strain rates (150 s-1). Using an inverse modelling approach, material parameters for an elastic constitutive model, with a stress-based fracture criterion were determined. The constitutive model was used in a finite element simulation of a high strain rate uniaxial compression test. Results obtained from the numerical model were in line with the experimental results.
Mechanical behaviour modelling under dynamic conditions: Application to structural and high strength steels
Authors: Simon Pierre , Demarty Yaël , Rusinek Alexis
Published: September 2018

Current needs in the design and optimization of complex ballistic protection structures lead to the development of more and more accurate numerical modelling for high impact velocity. The aim of developing such a tool is to be able to predict the protection performance of structures using few experiments. Considering only numerical approach, most important issue to have a reliable simulation is to focus on material behaviour description in term of constitutive relation and failure model for high strain rates, large field of temperatures and complex stress states. In this context, the study deals with the behaviour of two steels including a high strength steel and a structural steel. For this application, the materials can undergo both quasi-static and dynamic loading. Thus the strain rate range studied is varying from 10−3 to more than 103 s−1. Although the high strength steels do not exhibit high strain rate sensitivity, the temperature increases during dynamic loading is inducing thermal softening. Thus, temperature sensitivity is defined up to 500 K under quasi-static and dynamic conditions. Then, experiments are used to define the parameters of several constitutive relations like the Johnson-Cook model or the Rusinek Klepaczko model.
Behaviour of UHPFRCs in compression under high stress-rates
Authors: Cadoni Ezio , Dotta Matteo , Forni Daniele
Published: September 2018

The paper presents the results obtained on cylindrical Ultra High Performance Fibre Reinforced Concrete specimens with diameter of 30mm and a height of 60mm under compression at high stress rate (1.7–2.3 TPa/s). Four different percentages of fibre reinforcement are considered (1, 2, 3, and 4% fibre content) and compared with the results of the matrix (UHPC). A slight reduction of the strength and fracture time with the introduction of fibres is observed. The experimental results are analysed and discussed with the intent to better understand the mechanical behaviour of UHPFRC materials in case of dynamic event under service loading conditions.
Compression, Tension and Shear Testing of Fibrous Composite with the Split Hopkinson Bar Technique
Authors: Gilat Amos , Seidt Jeremy D.
Published: September 2018

The Split Hopkinson Bar (SHB) technique is used for high strain rate testing of T800/F3900 composite in compression, tension and shear. Digital Image Correlation (DIC) is used for measuring the full-field deformation on the surface of the specimen by using Shimadzu HPV-X2 high-speed video camera. Compression tests have been done on specimens machined from a unidirectional laminate in the 0°and 90° directions. Tensile tests were done in the 90° direction. Shear tests were done by using a notched specimen in a compression SHB apparatus. To study the effect of strain rate, quasi-static testing was also done using DIC and specimens with the same geometry as in the SHB tests. The results show that the DIC technique provides accurate strain measurements even at strains that are smaller than 1%. No strain rate effect is observed in compression in the 0° direction and significant strain rate effects are observed in compression and tension in the 90° direction, and in shear.
Poisson‘s Ratio Induced Radial Inertia Confinement During Dynamic Compression of Hyperelastic Foams
Authors: Sanborn Brett , Song Bo , Lu Wei-Yang
Published: September 2018

Hyperelastic foams have excellent impact energy absorption capability and can experience full recovery following impact loading. Consequently, hyperelastic foams are selected for different applications as shock isolators. Obtaining accurate intrinsic dynamic compressive properties of the hyperelastic foams has become a crucial step in shock isolation design and evaluation. Radial inertia is a key issue in dynamic characterization of soft materials. Radial inertia induced stress in the sample is generally caused by axial acceleration and large deformation applied to a soft specimen. In this study, Poisson’s ratio of a typical hyperelastic foam – silicone foam – was experimentally characterized under high strain rate loading and was observed to drastically change across the densification process. A transition in the Poisson’s ratio of the silicone foam specimen during dynamic compression generated radial inertia which consequently resulted in additional axial stress in the silicone foam sample. A new analytical method was developed to address the Poisson’s ratio-induced radial inertia effects for hyperelastic foams during high rate compression.
Variability of the effective strain rate in SHTB tests and related effects on the dynamic stress amplification
Authors: Mirone Giuseppe , Barbagallo Raffaele
Published: September 2018

Although the standard procedure for SHTB testing is based on the hypothesis that the strain rate is nominally constant during each test, it is known by many experimental evidences that the effective strain rate histories cannot be really constant, and this may cause the function expressing the dynamic amplification of the stress to substantially differ from that inferred under the hypothesis of strain rate constancy. This aspect is stressed out in this work by experiments and by numerical analyses, relating the variability of the strain rate to the finite rise time necessary in Hopkinson bars for reaching the plateau of the loading wave, and to the abrupt large increase in the effective strain rate naturally induced by the necking onset. Also the interplay between the achievement of the strain rate plateau and the achievement of the necking initiation strain is analysed, for assessing if and eventually how the same strain rate plateau achieved before or after the necking onset can affect the resulting dynamic amplification of the stress17 mm from the left and right page margins and justified..
Towards Standardising SHPB Testing - A Round Robin Exercise
Authors: Govender Reuben , Kariem Muhammad , Ruan Dong , Santiago Rafael , Wei Shu Dong , Alves Marcilio , Lu Guoxing , Nurick Gerald , Langdon Genevieve
Published: September 2018

The Split Hopkinson Pressure Bar (SHPB) test, while widely utilised for high strain rate tests, has yet to be standardised. As an exploratory step towards developing a standard test method or protocol, a Round Robin test series has been conducted between four institutions: (i) Swinburne University of Technology, Australia (ii) University of São Paulo, Brazil, (iii) University of Cape Town, South African and (iv) Nanyang Technological University, Singapore. Each institution prepared specimens from a metallic material, and provided batches of specimens from their chosen material to the other institutions. The materials utilised in this round of testing were commercially pure copper and aluminium, magnesium alloy and stainless steel (316 grade). The intent of the first exercise is to establish the consistency of SHPB test results on nominally identical specimens at comparable elevated strain rates, conducted by different laboratories following notionally similar test procedures with some freedom in data processing. This paper presents and compares the results of the first batch of tests for copper, identifying variations between results from different laboratories. The variation between different laboratories’ results for copper is suffciently small that there is confidence in the potential to develop a draft standard in future.
Hypervelocity impact phenomena of LPSO-magnesium alloys
Authors: Nishida Masahiro , Kodama Fumiya , Hayashi Koichi , Akahoshi Yasuhiro , Hokamoto Kazuyuki , Kawamura Yoshihito
Published: September 2018

Hypervelocity impact phenomena of long period stacking ordered type magnesium alloys (LPSO-Mg) plates were examined at the impact velocities of 4 km/s and 6 km/s. Ejecta veil and external bubble of debris of LPSO-Mg were darker than those of aluminum alloy A6061-T6. The size of external bubble of debris of LPSO-Mg was slightly smaller than that of A6061-T6. The velocity reduction of LPSOMg was slightly larger than that of A6061-T6. However, the scatter area of projectile and targets were not determined by electron probe micro-analyzer.