bluuebunny/crossref_metadata_2025 huggingface dataset:
Gamma-ray glow preceding downward terrestrial gamma-ray flash
Authors: Wada Yuuki , Enoto Teruaki , Nakamura Yoshitaka , Furuta Yoshihiro , Yuasa Takayuki , Nakazawa Kazuhiro , Morimoto Takeshi , Sato Mitsuteru , Matsumoto Takahiro , Yonetoku Daisuke , Sawano Tatsuya , Sakai Hideo , Kamogawa Masashi , Ushio Tomoo , Makishima Kazuo , Tsuchiya Harufumi
Published: June 2019

Two types of high-energy events have been detected from thunderstorms. One is “terrestrial gamma-ray flashes” (TGFs), sub-millisecond emissions coinciding with lightning discharges. The other is minute-lasting “gamma-ray glows”. Although both phenomena are thought to originate from relativistic runaway electron avalanches in strong electric fields, the connection between them is not well understood. Here we report unequivocal simultaneous detection of a gamma-ray glow termination and a downward TGF, observed from the ground. During a winter thunderstorm in Japan on 9 January 2018, our detectors caught a gamma-ray glow, which moved for ~100 s with ambient wind, and then abruptly ceased with a lightning discharge. Simultaneously, the detectors observed photonuclear reactions triggered by a downward TGF, whose radio pulse was located within ~1 km from where the glow ceased. It is suggested that the highly-electrified region producing the glow was related to the initiation of the downward TGF.
Stochastic dynamics and pattern formation of geometrically confined skyrmions
Authors: Schäffer Alexander F. , Rózsa Levente , Berakdar Jamal , Vedmedenko Elena Y. , Wiesendanger Roland
Published: June 2019

Ensembles of magnetic skyrmions in confined geometries are shown to exhibit thermally driven motion on two different time scales. The intrinsic fluctuating dynamics (t ∼ 1 ps) are governed by short-range symmetric and antisymmetric exchange interactions, whereas the long-time limit (t ≳ 10 ns) is determined by the coaction of skyrmion–skyrmion-repulsion and the system’s geometry. Micromagnetic simulations for realistic island shapes and sizes are performed and analyzed, indicating the special importance of skyrmion dynamics at finite temperatures. We demonstrate how the competition between skyrmion mobility and observation time directly affects the addressability of skyrmionic bits, which is a key challenge on the path of developing skyrmion-based room-temperature applications. The presented quasiparticle Monte Carlo approach offers a computationally efficient description of the diffusive motion of skyrmion ensembles in confined geometries, like racetrack memory setups.
Comment on “Hierarchically porous, ultra-strong reduced graphene oxide-cellulose nanocrystal sponges for exceptional adsorption of water contaminants” by N. Yousefi, K. K. W. Wong, Z. Hosseinidoust, H. O. Sørensen, S. Bruns, Y. Zheng and N. Tufenkji, Nanoscale, 2018, 10, 7171
Authors: Ma Jie , Xiong Yuecheng , Yu Fei
Published: June 2019

The MB-spot test is susceptible to multiple factors leading to inaccurate SSA characterization.
Determination of the platelet-derived growth factor BB by a sandwich format thrombin-linked aptamer assay on a microplate
Authors: Guo Limin
Published: June 2019

Microplate based assays have advantages such as rapid detection and high throughput analysis.
Solvent-dependent, rhodium catalysed rearrangement reactions of sulfur ylides
Authors: Yang Zhen , Guo Yujing , Koenigs Rene M.
Published: June 2019

Depending on the solvent used, benzyl sulfides undergo in the presence of a rhodium(ii) catalyst either [1,2]- or [2,3]-sigmatropic rearrangement.
A nitroxyl-responsive near-infrared fluorescent chemosensor for visualizing H2S/NO crosstalk in biological systems
Authors: Yang Mingwang , Fan Jiangli , Sun Wen , Du Jianjun , Long Saran , Shao Kun , Peng Xiaojun
Published: June 2019

A robust and reductant-resistant NIR fluorescent probe was developed to visualize NO/H2S crosstalk through detecting nitroxyl in living cells and tissues.
In situ formed [M(CN)9] (M = W, Mo) as a building block for the construction of two nona-cyanometalate-bridged heterometallic coordination polymers
Authors: Qian Jun , Yoshikawa Hirofumi , Humphrey Mark G. , Zhang Jinfang , Awaga Kunio , Zhang Chi
Published: June 2019

Two 3D cyano-bridged coordination polymers are constructed from in situ generated nona-cyanometalate [M(CN)9] (M = W, Mo) connected dpo ligands and Mn ions.
Photodissociation dynamics and the dissociation energy of vanadium monoxide, VO, investigated using velocity map imaging
Authors: Gentleman Alexander S. , Iskra Andreas , Köckert Hansjochen , Mackenzie Stuart R.
Published: June 2019

Velocity map imaging has been employed to study multi-photon fragmentation of vanadium monoxide (VO) via the C 4Σ− state.
Lithium oxide: a quantum-corrected and classical Monte Carlo study
Authors: Lavrentiev M. Yu. , Allan N. L. , Wragg C.
Published: June 2019

Quantum corrections to unit cell parameters provide correct low-temperature limits and must be allowed for when comparing theory and experiment.
Shiga toxin binding alters lipid packing and the domain structure of Gb3-containing membranes: a solid-state NMR study
Authors: Bosse Mathias , Sibold Jeremias , Scheidt Holger A. , Patalag Lukas J. , Kettelhoit Katharina , Ries Annika , Werz Daniel B. , Steinem Claudia , Huster Daniel
Published: June 2019

The individual response of various lipid species to shiga toxin binding to the membrane was studied by2H NMR.
Mechanistic insight into E22Q-mutation-induced antiparallel-to-parallel β-sheet transition of Aβ16−22fibrils: an all-atom simulation study
Authors: Li Xuhua , Lei Jiangtao , Qi Ruxi , Xie Luogang , Wei Guanghong
Published: June 2019

E22Q mutation of Aβ16−22fibrils facilitates parallel β-sheet formation by enhancing Q22–Q22 hydrogen-bonding interaction and A21–A21, F20–F20, F19–F19 and V18–V18 hydrophobic interaction.
Engineering of highly active Au/Pd supported on hydrogenated urchin-like yolk@shell TiO2 for visible light photocatalytic Suzuki coupling
Authors: Rohani Sahar , Ziarati Abolfazl , Ziarani Ghodsi Mohammadi , Badiei Alireza , Burgi Thomas
Published: June 2019

An engineered hydrogenated urchin-like yolk@shell TiO2 structure decorated with Au/Pd nanoparticles was designed via sequential steps and employed in visible light photocatalytic Suzuki coupling.
Insights into melanoidin conversion into fluorescent nanoparticles in the Maillard reaction
Authors: Li Dongmei , Xie Yisha , Na Xiaokang , Li Yao , Dai Chengbo , Li Yulian , Tan Mingqian
Published: June 2019

Melanoidins are not the final product of the Maillard reaction, and they can be further converted to fluorescent nanoparticles after hydrothermal treatment.
Quantitative proteomic analysis of milk fat globule membrane (MFGM) proteins from donkey colostrum and mature milk
Authors: Li Weixuan , Li Mohan , Cao Xueyan , Yang Mei , Han Hongjiao , Kong Fanhua , Yue Xiqing
Published: June 2019

The composition and functions of milk fat globule membrane (MFGM) proteins are important indicators of the nutritional quality of milk.
Potential effects of rapeseed peptide Maillard reaction products on aging-related disorder attenuation and gut microbiota modulation in d-galactose induced aging mice
Authors: He Shudong , Zhang Zuoyong , Sun Hanju , Zhu Yuchen , Cao Xiaodong , Ye Yongkang , Wang Junhui , Cao Yanping
Published: June 2019

Rapeseed peptide Maillard reaction products (MRPs) were developed, and the effects of MRPs on d-galactose induced aging Kunming mice were investigated for 6 weeks with low, medium and high doses of 200, 400, 800 mg Kg−1 day−1, respectively.
The potential use of modified quinoa protein isolates in cupcakes: physicochemical properties, structure and stability of cupcakes
Authors: López-Alarcón Cyndy A. , Cerdán-Leal Martín A. , Beristain César I. , Pascual-Pineda Luz A. , Azuara Ebner , Jiménez-Fernández Maribel
Published: June 2019

The objective of this study was to evaluate the physicochemical, textural, sensory and microbiological stability of cupcakes added with different proportions of modified quinoa protein isolate.
Antioxidant dietary fiber isolated from spent coffee (Coffea arabica L.) grounds improves chronotype and circadian locomotor activity in young adults
Authors: Oseguera-Castro Karla Y. , Madrid Juan A. , Martínez Madrid María José , García Olga P. , del Castillo Maria Dolores , Campos-Vega Rocio
Published: June 2019

This study shows for the first time, the modulation of the circadian rhythm and the positive chronobiotic effects of humans, by a dietary intervention, in daily life, with food or dietary fiber source.
Atomic spectrometry update: review of advances in elemental speciation
Authors: Clough Robert , Harrington Chris F. , Hill Steve J. , Madrid Yolanda , Tyson Julian F.
Published: June 2019

This review covers advances in elemental speciation by a range of coupled techniques, including HPLC-ICP-MS, HPLC-HG-AFS and GC-ICP-MS.
Potassium manganese hexacyanoferrate/graphene as a high-performance cathode for potassium-ion batteries
Authors: Sun Yunpo , Liu Chunli , Xie Jian , Zhuang Dagao , Zheng Wenquan , Zhao Xinbing
Published: June 2019

A potassium manganese Prussian blue/graphene nanocomposite exhibits a high capacity, excellent rate capability and long high-rate cycle life.
Synthesis, characterization, DFT calculations and anticancer activity of a new oxidovanadium(iv) complex with a ligand derived from o-vanillin and thiophene
Authors: Rodríguez María R. , Balsa Lucía M. , Del Plá Julián , García-Tojal Javier , Pis-Diez Reinaldo , Parajón-Costa Beatriz S. , León Ignacio E. , González-Baró Ana C.
Published: June 2019

New vanadium complex was synthesized and fully characterized showing promising anticancer activity on triple negative breast cancer cells.
A high-sensitivity fluorescent probe with a self-immolative spacer for real-time ratiometric detection and imaging of alkaline phosphatase activity
Authors: Zhang Xueyan , Chen Xiangzhu , Zhang Yuanyuan , Gao Gui , Huang Xiaoqian , Hou Shicong , Ma Xiaodong
Published: June 2019

The probe APW uses a self-immolative mechanism to achieve a ratio response to ALP, which has the following advantages: fast response (in less than 15 min), high quantum yield (Φ = 0.6), low detection limit (0.46 U L−1) and excellent selectivity.
Macrophage-derived nanovesicles exert intrinsic anti-inflammatory properties and prolong survival in sepsis through a direct interaction with macrophages
Authors: Molinaro Roberto , Pastò Anna , Corbo Claudia , Taraballi Francesca , Giordano Federica , Martinez Jonathan O. , Zhao Picheng , Wang Xin , Zinger Assaf , Boada Christian , Hartman Kelly A. , Tasciotti Ennio
Published: June 2019

Here, we have demonstrated that biomimetic nanovesicles assembled from macrophages' membrane proteins are similar to macrophage-derived exosomes. The anti-inflammatory activity observed in vivo derives from their direct interaction with macrophages.
A computational study on the identity of the active catalyst structure for Ru(ii) carboxylate assisted C–H activation in acetonitrile
Authors: McMullin Claire L. , Rajabi Nasir A. , Hammerton James S.
Published: June 2019

Density Functional Theory (DFT) calculations using a consistent methodology accounting for solvation, dispersion and thermal effects have been used to study C–H activation of the simple directing group substrate 2-phenylpyridine (a-H).
Design and application of diimine-based copper(i) complexes in photoredox catalysis
Authors: Földesi Tamás , Sipos Gellért , Adamik Réka , Nagy Bálint , Tóth Balázs L. , Bényei Attila , Szekeres Krisztina J. , Láng Győző G. , Demeter Attila , Peelen Timothy J. , Novák Zoltán
Published: June 2019

Novel copper catalysts were designed, synthesized and utilized in visible light-driven photocatalytic ATRA reactions.
Alcohol mediated degenerate chain transfer controlled cationic polymerisation of para-alkoxystyrene
Authors: Prasher Alka , Hu Huamin , Tanaka Joji , Nicewicz David A. , You Wei
Published: June 2019

In this report we demonstrate methanol as an effective degenerative chain transfer agent to control the cationic polymerisation (initiated by triflic acid) of electron rich p-alkoxy-styrenes, such as p-methoxystyrene (p-MOS).
Experimental investigation on strength development of lime stabilized loess
Authors: Jia Liang , Guo Jian , Zhou Zhidong , Fu Yong , Yao Kai
Published: June 2019

Lime stabilization has been widely used in pavement subbases and ground improvement, but the investigation of the mechanical properties and the microstructure of lime stabilized loess is still insufficient.
Conversion of woody oil into bio-oil in a downdraft reactor using a novel silicon carbide foam supported MCM41 composite catalyst
Authors: Yu Zhenting , Wang Yunpu , Jiang Lin , Dai Leilei , Liu Yuhuan , Ruan Roger , Wen Pingwei , Zhao Yunfeng , Duan Dengle , Zou Rongge , Wu Qiuhao , Li Yanzhi
Published: June 2019

Main flow chart of the pyrolysis process using SiC-MCM41 catalyst.
A fluorescence sensing platform of theophylline based on the interaction of RNA aptamer with graphene oxide
Authors: Wu Jian-Feng , Gao Xin , Ge Ling , Zhao Guang-Chao , Wang Guang-Feng
Published: June 2019

A fluorescent sensing platform of theophylline based on the interaction of an RNA aptamer with GO and CdTe as the signal.
Deposition amount and dissipation kinetics of difenoconazole and propiconazole applied on banana with two commercial spray adjuvants
Authors: Xu Jin , Long Xiaofang , Ge Shijia , Li Mengli , Chen Lingzhu , Hu Deyu , Zhang Yuping
Published: June 2019

The effect of adding organosilicon and mineral oil adjuvants after being applied to the residues of difenoconazole and propiconazole in banana leaves was studied. The partition of the pesticides between soil, leaves and fruits was evaluated.
Preparation of monoethyl fumarate-based molecularly imprinted polymers and their application as a solid-phase extraction sorbent for the separation of scopolamine from tropane alkaloids
Authors: Zuo Jie , Zhang Xingyuan , Li Xinyu , Li Zhiwei , Li Zongren , Li Honghong , Zhang Wencheng
Published: June 2019

Monoethyl fumarate with two functional groups was introduced to prepare a MIP for the separation of scopolamine from tropane alkaloids.
Factors affecting the efficiency of a bioelectrochemical system: a review
Authors: Zhang Xiaolin , Li Xiaojing , Zhao Xiaodong , Li Yongtao
Published: June 2019

The great potential of bioelectrochemical systems (BESs) in pollution control combined with energy recovery has attracted increasing attention.
Impact of basic arithmetic skills on success in first-semester general chemistry
Authors: Williamson Vickie M. , Walker Deborah Rush , Chuu Eric , Broadway Susan , Mamiya Blain , Powell Cynthia B. , Shelton G. Robert , Weber Rebecca , Dabney Alan R. , Mason Diana
Published: June 2019

First-semester general chemistry is a known “gatekeeper” course due to its high failure rate. These higher education courses are taken by students who for the most part are regularly admitted freshmen, yet many struggle to succeed. In this investigation researchers from six higher-education institutions of varied sizes with student bodies of different ethnic composition teamed up to investigate the Math-Up Skills Test (MUST) as a potential tool to identify at-risk students in first-semester general chemistry (Chem I). A large population (N = 1073) was given the MUST at the beginning of the semester. The MUST had good internal consistency with the sample (Cronbach's alpha = 0.856). The MUST offers a quick 15 minute assessment of basic mathematics ability without a calculator. Instructors may find it easier than other documented predictors, which may take more time or involve obtaining student records (e.g., Math SAT). Results from the MUST support prior findings that mathematics skills correlate with course grades in chemistry. Poor arithmetic automaticity may be an underlying factor in lower performance by many students. With statistical modeling, the MUST, along with other demographic variables, was able to identify students who would go on to make a 69.5% or better in Chem I with a high percent of accuracy. The MUST, in tandem with other demographic variables, should be considered a potential tool for early identification of students at-risk for failing the class.
Structural and defect engineering of cobaltosic oxide nanoarchitectures as an ultrahigh energy density and super durable cathode for Zn-based batteries
Authors: Teng Chunlin , Yang Fan , Sun Minghui , Yin Keshu , Huang Qintong , Fu Guangying , Zhang Chuanqi , Lu Xihong , Jiang Jiuxing
Published: June 2019

Ordered mesoporous and oxygen-vacancy are demonstrated to significantly improve the electrochemical performance of Co3O4. Capitalizing on the optimized M-Co3O4−x cathode, the ZBB exhibits ultrahigh energy density and extraordinary cycling stability.
The capillary interaction between pairs of granular rafts
Authors: Lagarde Antoine , Josserand Christophe , Protière Suzie
Published: June 2019

The interaction between two granular rafts at an interface strongly depends on their respective number of particles.
Effect of trace hydrofluoric acid in a LiPF6 electrolyte on the performance of a Li–organic battery with an N-heterocycle based conjugated microporous polymer as the cathode
Authors: Chen Zhangxin , Xu Ning , Li Weijun , Zhao Ruiyang , Dong Yujie , Liu Junlei , Su Chang , Wang Jianli , Zhang Cheng
Published: June 2019

A novel electrochemical test confirms the acid-doping of trace HF into N-heterocycle based polymers in a LiPF6 electrolyte.
Three-dimensional SWCNT and MWCNT hybrid networks for extremely high-loading and high rate cathode materials
Authors: Kim Dae-wook , Zettsu Nobuyuki , Teshima Katsuya
Published: June 2019

Extremely high-loading LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode materials (up to 99.5 wt%) were achieved through self-organization of a three-dimensional network of multi-walled and single-walled CNT hybrids.
Electrochemically modified graphite paper as an advanced electrode substrate for supercapacitor application
Authors: Mandal Debasish , Routh Parimal , Mahato Ashok K. , Nandi Arun K.
Published: June 2019

The designed electrochemically modified graphite paper (ECM-GP) having a foam-like structure serves as an advanced electrode substrate of supercapacitors.
Self-supported multidimensional Ni–Fe phosphide networks with holey nanosheets for high-performance all-solid-state supercapacitors
Authors: Li Shuo , Hua Minghao , Yang Yuan , Huang Wei , Lin Xiaohang , Ci Lijie , Lou Jun , Si Pengchao
Published: June 2019

Comprehensive research of the chemosynthesis, electrochemical behavior and DFT calculations of a multidimensional Ni–Fe–P electrode for all-solid-state supercapacitors.
Discovering a selective semimetal element to increase hematite photoanode charge separation efficiency
Authors: Nogueira André Esteves , Santos Soares Mario Rodrigo , Souza Junior João Batista , Ospina Ramirez Carlos Alberto , Souza Flavio Leandro , Leite Edson Roberto
Published: June 2019

A colloidal deposition process combined with the thermal spreading ability of Sb over hematite surface is used to obtain a mesoporous photoanode for water oxidation.
Tin(iv) dopant removal through anti-solvent engineering enabling tin based perovskite solar cells with high charge carrier mobilities
Authors: Bandara R. M. I. , Jayawardena K. D. G. I. , Adeyemo S. O. , Hinder S. J. , Smith J. A. , Thirimanne H. M. , Wong N. C. , Amin F. M. , Freestone B. G. , Parnell A. J. , Lidzey D. G. , Joyce H. J. , Sporea R. A. , Silva S. R. P.
Published: June 2019

We report the need for careful selection of anti-solvents for Sn-based perovskite solar cells fabricated through the commonly used anti-solvent method, compared to their Pb-based counterparts.
Electric field-tailored giant transformation of magnetic anisotropy and interfacial spin coupling in epitaxial γ′-Fe4N/Pb(Mg1/3Nb2/3)0.7Ti0.3O3(011) multiferroic heterostructures
Authors: Lai Zhengxun , Li Chunlei , Li Zirun , Liu Xiang , Zhou Ziyao , Mi Wenbo , Liu Ming
Published: June 2019

By spin-dependent screening effect-induced magnetoelectric coupling, magnetization can be largely controlled by electric fields without an auxiliary magnetic field.
Mass-produced SEBS/graphite nanoplatelet composites with a segregated structure for highly stretchable and recyclable strain sensors
Authors: Shen Ziming , Feng Jiachun
Published: June 2019

By utilizing the micro-size characteristic of as-received SEBS powders and the ability of GNPs to attach to their surface, SEBS/GNP composites with a segregated structure were prepared for highly stretchable and recyclable strain sensors.
Locking excitons in two-dimensional emitting layers for efficient monochrome and white organic light-emitting diodes
Authors: Liu Yuan , Hänisch Christian , Wu Zhongbin , Will Paul-Anton , Fries Felix , Wu Jinhan , Lenk Simone , Leo Karl , Reineke Sebastian
Published: June 2019

Organic light-emitting diodes combine ultra-thin non-doped emitting layers for simplified and flexible design and charge-transfer-type recombination layers for exciton management.
Biologically inspired adaptive intelligent secondary control for MGs under cyber imperfections
Authors: Jafari Mohammad , Ghasemkhani Amir , Sarfi Vahid , Livani Hanif , Yang Lei , Xu Hao
Published: June 2019

In this study, the authors investigate the secondary control of microgrids (MGs) in the presence of cyber imperfections such as delay and/or noise, and system disturbances. The existence of cyber imperfections and disturbance could bring in system uncertainty that will seriously degrade the effectiveness of most existing secondary control such as proportional–integral–derivative (PID), etc. To tackle these issues, a biologically‐inspired reinforcement learning technique has been proposed which adjusts its parameters to the perturbed system setpoints generated by the cyber imperfections and system disturbances. The learning capability and low computational complexity of the proposed controller make it a promising approach to take cyber imperfections and system disturbances into account, where traditional control methodologies are not suitable due to their vulnerability to the cyber imperfections. First, an emotional learning‐based secondary control structure is proposed, where the impacts of cyber imperfection and disturbance have been captured efficiently. Then, the real‐time update laws are developed for generating the proper emotional signals (ESs) to stabilize the frequency and voltage. Ultimately, using the generated ESs, the secondary control of MGs is achieved. The Lyapunov analysis has been provided to prove the stability of the proposed design. Moreover, MATLAB/Simulink‐based simulations demonstrate the effectiveness of the proposed algorithm.
Abundances of sulphur molecules in the Horsehead nebula
Authors: Rivière-Marichalar P. , Fuente A. , Goicoechea J. R. , Pety J. , Le Gal R. , Gratier P. , Guzmán V. , Roueff E. , Loison J. C. , Wakelam V. , Gerin M.
Published: June 2019

Context. Sulphur is one of the most abundant elements in the Universe (S/H ~ 1.3 × 10−5) and plays a crucial role in biological systems on Earth. The understanding of its chemistry is therefore of major importance.

Aims. Our goal is to complete the inventory of S-bearing molecules and their abundances in the prototypical photodissociation region (PDR) the Horsehead nebula to gain insight into sulphur chemistry in UV irradiated regions. Based on the WHISPER (Wide-band High-resolution Iram-30 m Surveys at two positions with Emir Receivers) millimeter (mm) line survey, our goal is to provide an improved and more accurate description of sulphur species and their abundances towards the core and PDR positions in the Horsehead.

Methods. The Monte Carlo Markov chain (MCMC) methodology and the molecular excitation and radiative transfer code RADEX were used to explore the parameter space and determine physical conditions and beam-averaged molecular abundances.

Results. A total of 13 S-bearing species (CS, SO, SO2, OCS, H2CS – both ortho and para – HDCS, C2S, HCS+, SO+, H2S, S2H, NS and NS+) have been detected in the two targeted positions. This is the first detection of SO+ in the Horsehead and the first detection of NS+ in any PDR. We find a differentiated chemical behaviour between C–S and O–S bearing species within the nebula. The C–S bearing species C2S and o-H2CS present fractional abundances a factor of > two higher in the core than in the PDR. In contrast, the O–S bearing molecules SO, SO2, and OCS present similar abundances towards both positions. A few molecules, SO+, NS, and NS+, are more abundant towards the PDR than towards the core, and could be considered as PDR tracers.

Conclusions. This is the first complete study of S-bearing species towards a PDR. Our study shows that CS, SO, and H2S are the most abundant S-bearing molecules in the PDR with abundances of approximately a few 10−9. We recall that SH, SH+, S, and S+ are not observable at the wavelengths covered by the WHISPER survey. At the spatial scale of our observations, the total abundance of S atoms locked in the detected species is <10−8, only ~0.1% of the cosmic sulphur abundance.
Swelling properties of a Danish Paleogene clay: a multiscale study on structure
Authors: Di Remigio Giorgia , Rocchi Irene , Zania Varvara
Published: June 2019

Paleogene clays are highly plastic, stiff clays deposited between 65.5 and 43 millions of years ago, frequently met in northern Europe. As they were deposited before the Quaternary, they experienced the glacial cycles that occurred in that period. The evolution and movement of the ice masses above the Paleogene clays highly influenced their stress history. During the interglacial periods the glaciers melted, unloading the underlying formations while during the glacial periods the glaciers mass loaded the Paleogene clays and sheared their shallower layers. Previous studies examined the compressibility and swelling of Danish Paleogene clays, and showed an early preconsolidation stresses, lower than that associated with the overburden pressure. This phenomenon was attributed to the effects of the glaciers movements. Other factors that have not been investigated yet and influence the deformation behaviour, can be associated with the micro and nano structure, meaning the particle orientation, and the mineralogical composition of the clays. This study focuses on a Danish Paleogene Formation called Røsnæs clay and the aim is to investigate the macromechanical swelling behaviour and its relation with particle rearrangement. A combination of 1D compression tests, microscopy imaging, mercury intrusion porosimetry and X-ray diffraction tests were performed on reconstituted and undisturbed samples in order to investigate the fabric, the pore structure and the mineralogy of the soil. A synthetic saline solution reproducing the in situ water was used to prepare the reconstituted samples and for the water bath. Variations with the swelling index were correlated with the clay particles rearrangement taking in to account the mineralogical composition. The compression curves and the scanning electron microscope micrographs were correlated with the mercury intrusion porosimeter results.
Development of vertical and horizontal disk transducers for wave velocity measurements in a large rectangular specimen
Authors: Dutta Troyee Tanu , Otsubo Masahide , Kuwano Reiko , Sato Takeshi
Published: June 2019

For the accurate design of structures subjected to both static and dynamic loadings, elastic wave velocity and small strain stiffness are essential parameters. Numerous techniques have been developed to estimate wave velocities of geomaterials. Bender elements which are widely adopted for wave velocity measurements are invasive in nature and are not suitable for coarse-grained materials. In the present study, new design configuration of disk transducer has been introduced to measure both vertical and horizontal wave velocities for coarse granular soils considering multidirectional oscillation of propagating waves. An innovative arrangement of both compression and shear type elements has been installed in a large-sized triaxial apparatus having rectangular specimens of size 236×236×500 mm to assess the wave velocities. The materials described are Toyoura sand (D50 = 0.24 mm) and Oiso gravel (D50 = 11.8 mm). This arrangement enables measurements of nine types of wave velocities, and thus the stiffness anisotropy to be quantified. For Oiso gravel, horizontal wave velocities are greater than vertical wave velocities for both shear and compression waves. For Toyoura sand, shear wave velocities are higher in horizontal direction of propagation, whereas similar compression wave velocities are observed from both horizontal and vertical directions.
Magnetic measurement system of sandy gravel specimens shape during tests in a large triaxial apparatus
Authors: Ventini Roberta , Flora Alessandro , Lirer Stefania , Mancuso Claudio
Published: June 2019

As well known, rockfill behaviour is strongly influenced by both intrinsic (mineralogy and size of particles, grain shapes, soil grading etc.) and state parameters (relative density, stress state, relative humidity). To investigate their mechanical response to stresses and relative humidity (RH) loadings, a large size triaxial device (H = 410 mm, D = 200 mm) has been developed at the University of Naples Federico II (Italy), including modifications required to impose partially saturated conditions in the specimen by means of the vapour equilibrium technique. In order to evaluate local axial and radial strains and global volumetric strains in partially saturated conditions, a magnetic shape detector device has been designed and installed. The accuracy of this system has been evaluated in some isotropic compression triaxial tests on compacted sandy-gravel specimens. The experimental data clearly show the effectiveness of the magnetic system in the measurement of axial displacements while the measurement in radial direction appear to be strongly affected by the non-linearity of the complex magnetic field generated during the test and requires further checking tests.
Indirect measurements of water content using TDR-inferred dielectric permittivity and electrical resistivity
Authors: de Carvalho Faria Lima Lopes Bruna , de Carvalho Faria Lima Lopes Laís , Tarantino Alessandro
Published: June 2019

The measurement of moisture distribution in Engineered Barrier Systems (EBS) in salt mines and deep geological disposals is essential in order to monitor fluid ingress and record data for long-term security analyses. Additionally, soil moisture content has influence over the mechanical properties of the soil as well as plant growth, soil stability and contaminant transport to cite some. Therefore, finding affordable and reliable ways to determine moisture content, quickly and in the field without sampling, is of great interested among people in different subject areas. Time-domain reflectometry (TDR) has become a recognized electromagnetic method for non-destructive measurement of dielectric permittivity and electrical conductivity of moist porous materials. It turns out that both these measurements depend on the material moisture content, among other things. This paper presents a series of calibration tests performed on soil samples. TDR probes were used to obtain the dielectric permittivity and electrical conductivity of the samples. As a consequence, relationships between these measurements and the samples' volumetric water content were later established. These relationships can then be used to indirectly determine that important information of water content on similar soil material using cheap, quick and non-destructive TDR probes.
Quality assessment of a new in-mould slurry deposition method for triaxial specimen reconstitution of clean and silty sands
Authors: Dominguez-Quintans Camelia , Quinteros V. Santiago , Carraro J. Antonio H. , Zdravkovic Lidija , Jardine Richard J.
Published: June 2019

An innovative specimen reconstitution technique for sandy and silty soils that simulates underwater deposition is presented and evaluated. The technique is an upgraded version for triaxial testing of the well-established slurry deposition method. This novel setup integrates the reconstitution mould and the mixing tube into a single unit to avoid transferring the sample from the mixing tube to the mould. This subtle, but critical, modification enables reconstitution of very loose specimens as sample transfer disturbance, which can be significant, is eliminated. The quality of specimens prepared by the new reconstitution method was assessed by experiments on a clean sand from the UK (Ham River sand) and a silty sand from Norway (Øysand). The method, as any slurry-based procedure, is capable of producing homogeneous specimens with high initial degree of saturation, even in the absence of back pressure. The procedure is shown to be suitable for sands with or without fines. Moreover, the new method is able to achieve a wide range of initial void ratios, from very loose to very dense, without imposing any particle crushing in the latter case.
One-dimensional consolidation of overconsolidated clay using Constant Rate of Strain testing
Authors: Andries Joren , Verastegui Daniel , De Beule Kim , Baertsoen An
Published: June 2019

The main method for the determination of consolidation parameters in Flanders (Belgium) is still the incremental loading test (IL test). This method can take up to several weeks for some typical Flemish overconsolidated (OC) clays. In theory, the same relationship between settlement and vertical stress can be obtained by performing a constant rate of strain test (CRS test). The main advantages of a CRS test are that the data is continuous and that the test can often be completed considerably faster than an IL test. In this paper, results of both IL and CRS tests on two undisturbed stiff OC clay samples of the same geological formation (Maldegem formation deposited during the Paleogene period) were compared. CRS tests were performed based on ASTM D4186, but constant stress stages were controlled using effective vertical stress instead of total vertical stress as most important adjustment to the standard. In addition, special attention was paid to the development of initial swell pressure and selecting an appropriate rate of strain for this clay with a very high plasticity. Similar values for compressibility and hydraulic conductivity were found using both IL and CRS test results. As the duration of a CRS test on this clay with low hydraulic conductivity can also take up to a few weeks, the time saving aspect of the test was found to be limited for the stiff OC clay tested. The uncertainty in estimating the pre-consolidation pressure and swell pressure was smaller using the continuous CRS test results.
Seepage test by HCA for remolded kaolin
Authors: Zhou Jian , Xu Jie , Luo Linghui , Yu Lianggui , Gong Xiaonan
Published: June 2019

Permeability is an import character of soil, especially in excavation and tunnelling. Hollow cylindrical apparatus (HCA) is often used to determine soil anisotropy, particularly soil strength and stiffness under different directions of major principal stress, so complex stress paths can be simulated and the corresponding soil properties can be examined. It can also be used to determine the permeability coefficient if a special mode is added, therefore the seepage test can be expected. Owing to no seepage test has been conducted by HCA before, the complete procedure of HCA seepage tests after static and dynamic loading are respectively studied. And the seepage stability stage is discussed since only data in this stage are valid and reliable for permeability calculation. The results show that:1) when the difference in average permeability coefficient within unit time (3600 seconds) less than 2% in 24h, it is reliable to take the average permeability coefficient in this period as the ultimate permeability in static seepage test; 2) for dynamic test, if the average permeability in 3600 seconds varies with 5% in 24h, the average permeability coefficient in this period can be taken as the ultimate value. Research in this paper provides a solid foundation for HCA seepage test under complex stress paths.
Self-sealing capacity of argillite samples
Authors: Di Donna Alice , Charrier Pascal , Salager Simon , Bésuelle Pierre
Published: June 2019

Many countries are currently facing the issue of finding a proper solution to store radioactive wastes coming from nuclear energy production plants. The possibility to store them in underground tunnels is largely considered and investigated. In France, Andra (Agence Nationale pour la gestion des Déchets Radioactifs) selected the Callovo-Oxfordian rock clay (COx) situated in the Meuse/Haute Marne site (France) between 400 and 600 m depth as possible host rock deposit. The excavation of the storage tunnels is expected to create a fractured zone around galleries. However, the factures will be then gradually re-saturated by the underground water coming from the surrounding rock mass and the fractures are expected to self-seal in contact with water, thanks to the swelling potential of COx. The capacity of self-sealing of COx, i.e. closing of fractures after water contact and possibly restoring of hydraulic permeability, is thus of primary interest for the safety of the storage system with respect to water, gas and solutes transport. In the work presented in this paper, the self-sealing behaviour of the COx argillite was investigated through x-ray tomography. The tested samples show significantly different responses depending on the zone where they have been collected on site. The results of mineralogical analyses (x-ray diffraction) are used to understand the observed phenomena.
Investigation of fabric evolution using bidirectional shear wave velocity measurements
Authors: Fakharian Kazem , Hamedani Farzad Kaviani , Parandian Iman , Aghdam Morteza Jabbarpour
Published: June 2019

In order to characterise fabric evolution, continuous bidirectional shear wave velocity measurements are performed in vertical and horizontal directions (V&H) on triaxial soil specimens during shearing in which two horizontal piezo-electrics were mounted on samples using a new measurement technique. The specimens are prepared by wet tamping method and then subjected to strain-controlled compressional shearing under drained and undrained conditions. The shear wave velocities of all drained specimens initially increased as the loading commenced and then converged to a unique state in both horizontal and vertical directions. The shear wave velocity of undrained specimens on the other hand, for both horizontal and vertical directions initially decreased due to the rising of the excess pore water pressure and then gradually approached a unique shear wave velocity like drained specimens. The fabric condition or stiffness in V&H directions of all the examined drained and undrained specimens at critical state are found to be unique.
Characteristics of elastic waves passing through a flowable fill at early age
Authors: Han WooJin , Byun Yong-Hoon , Lee Jong-Sub
Published: June 2019

Elastic waves obtained from transducers are widely used to monitor the strength and integrity of cementitious materials. A pair of bender elements (BEs) and piezo disk elements (PDEs) embedded in a cuboid mould are applied to monitor elastic waves passing through a cementitious material known as a flowable fill at early age. The flowable fills used in this study are mixed with calcium sulfoaluminate cement, sand, silt, fly ash, water, and an accelerator. Compressional and shear waves acquired from the PDEs and BEs, respectively, are observed for up to 72 hrs. Results show that the compressional and shear wave velocities increased with curing time. The sensors can be used effectively to monitor the hardening characteristics of flowable fills at early age, and the BEs are particularly suitable for evaluating the hardening conditions of flowable fills as a result of the wide variation in shear wave velocities.
On the evaluation of yield stress of soils for debris flow analysis
Authors: Besso Carlos , Pereira de Campos Tácio Mauro
Published: June 2019

Debris flow materials behave as a fluid, hence its analysis requires rheological parameters such as yield stress and viscosity. Yield stress is associated to the start and the end of the mass movement downhill in the sense that it denotes the yield transition from the creep to the flow regime, i.e., passage from solid to fluid state. This paper presents an experimental study of the yield stress of a colluvium from Rio de Janeiro, through its determination in a modified set-up of the slump test and in a rotational parallel plate rheometer. Tests were performed in five different water contents above its liquidity limit, providing a fairly good relationship between yield stress and water content. While slump test provides yield stress related to the beginning of the movement (acceleration), rheometer results are related to flow's outset and stoppage. As a result, the percentual differences between yield stresses associated with acceleration and deceleration were less than 5% in all testes, which is related to the low hysteresis effect in the flow curves obtained in the rotational rheometer. Comparing the two methodologies, it is proposed a correction from rheometer to slump test results. Results obtained are compared with data presented in other studies involving soil's yield stress, showing a good acceptance of the slump test results as a cheap alternative to rheometers.
Diffuse and localized deformation of a porous Vosges sandstone in true triaxial conditions
Authors: Couture Cyrille-B. , Bésuelle Pierre
Published: June 2019

This work presents an experimental study on the diffuse and localized deformation mechanisms of a high porosity (20%) Vosges sandstone (Eastern France) subjected to different stress paths in the deviatoric plane. The experimental campaign was performed using a high pressure true triaxial apparatus (TTA) in which the three principal stresses are independently controlled. A series of 10 quasi-static, monotonous loading tests was performed at 2 constant mean stresses, in the brittle-ductile transition regime, and at five prescribed Lode angles, from axisymmetric compression (ASC) to axisymmetric extension (ASE), as a measure of the deformation mode. The failure surface in each deviatoric plane and changes in macroscopic measurements, such as deformation band angles tracked by full field digital image correlation (DIC) technology, indicate a clear effect of the Lode angle on a transition between the brittle and ductile regime, independent from the mean stress level.
Investigating the use of Boyle's Law to relate pore air pressures and volume changes in unsaturated triaxial samples
Authors: Kwa Katherine , Airey David
Published: June 2019

Measuring the volume changes of unsaturated triaxial soil samples is one of the main challenges when performing unsaturated triaxial tests. Under fully undrained conditions, Boyle's Law can be used to calculate the sample's volume changes caused by the compression of air, as Boyle's Law relates changes in volume to changes in pore air pressures within the sample. This method has been used to calculate the volumetric strains and pore air pressures in unsaturated samples tested under cyclic loading conditions. However, the volume changes calculated from using Boyle's Law and the increases in pore air pressures, have not been compared with the actual measured volume changes of unsaturated samples. This study presents the pore pressures and compares the measured and predicted volumetric strains calculated from using Boyle's Law, in unsaturated triaxial samples that were tested cyclically. In some cases, using Boyle's Law was found to be similar to the volume changes estimated from direct measurement, but sometimes the method did not appear to work. Reasons for the discrepancies will also be discussed.
Novel rapid measurement system of undisturbed soils water characteristics curve utilizing the continuous pressurization method
Authors: Alowaisy Adel , Yasufuku Noriyuki , Ishikura Ryohei , Hatakeyama Masanori , Kyono Shuu
Published: June 2019

Through this paper, a sampling methodology and a novel full automatic system adopting the continuous pressurization method which is capable of determining the Soil Water Characteristics Curve (SWCC) for both remoulded and undisturbed samples in a very short time were developed. The proposed system was validated by comparing the SWCCs of standard testing soils obtained using the developed system to the SWCCs obtained using a conventional method. Remoulded and undisturbed natural soil samples were tested, where the degree of disturbance influence on the obtained SWCC was discussed. In addition, the undisturbed samples containing moulds material influence on the obtained SWCC was investigated. It was found that remoulded samples do not properly represent the in-situ conditions with significant error that should be carefully considered when conducting analysis and proposing countermeasures against unsaturated soils related Geo-disasters. In addition, the material which the containing mould is made from has minor influence on the obtained SWCC which can be neglected. Finally, it can be concluded that the developed undisturbed soil water characteristics curve obtaining system is direct, rapid, reliable and simple. In addition, the proposed undisturbed sampling and testing methodology can be used to accurately evaluate the spatial variations of the SWCC regardless the heterogeneity of the soil profile.
The effect of confinement in liquefaction tests carried out in a cyclic simple shear apparatus
Authors: Mele Lucia , Lirer Stefania , Flora Alessandro
Published: June 2019

The cyclic simple shear tests can be used to reproduce in laboratory the complex behaviour of the soil during an earthquake, simulating the continuous rotation of the principal stress axes. In this research a comparison of results between cyclic simple shear tests carried out with confining pressure or confining rings is reported. A cyclic simple shear apparatus is used to carry out tests with confining rings (the conventional way to carry out cyclic simple shear tests) and with a confining pressure applied to the specimen through pressurized water, where the K0 condition during consolidation is guaranteed by a sophisticated control system. The apparatus, in both the configurations, is described in detail. All tests were carried out on reconstituted specimens of an Italian sand with similar initial conditions, such as low relative density and confining pressure. All experimental results are reported in the plane cyclic stress ratio (CSR) and number of cycles where liquefaction occurs (Nliq) in order to evaluate the effect of confinement on the liquefaction resistance of the studied sand.
Undrained response of Sydney sand under non-reversal cyclic loading
Authors: Mohammadi Amirabbas , Airey David
Published: June 2019

Stress history and loading path can significantly influence the cyclic response of sands. It is well known that cyclic behaviour under non-symmetrical cycling is generally different from that under symmetrical loading around zero deviator stress. Anisotropic consolidation prior to cycling in triaxial apparatus changes the behaviour by exerting an initial static shear stress on critical planes. The present paper reports the results from a number of cyclic triaxial tests on anisotropically consolidated samples of Sydney beach sand. The samples are reconstituted in the laboratory and subjected to non-reversal cycling in compression only loading under undrained conditions. Typical test behaviours are described and the effects of cyclic stress ratio and initial state on the response are discussed. It is shown that the state parameter is capable of predicting the cyclic resistance and the trend of excess pore water pressure generation during one-way compressional cycling and, as has been well established for simple loading paths, critical state soil mechanics is able to provide a reliable framework to characterize the behaviour under different cyclic loading conditions.