bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of long-term natural aging to artificial aging in Duralumin
Authors: Brunet Magali , Malard Benoit , Ratel-Ramond Nicolas , Deshayes Christophe , Warot-Fonrose Bénédicte , Sciau Philippe , Douin Joël
Published: November 2020

The understanding of long-term aging of aeronautical materials, in particular aluminium alloys used in the fuselage and structure of aircraft is of extreme importance for airline fleets. In this work, a plate from an old aircraft (Breguet) was retrieved and studied in terms of microstructure and mechanical properties. A comparison was made between this naturally-aged alloy and a modern alloy on which different artificial aging conditions were applied. The old alloy exhibits a precipitation of θ-Al2Cu at grain boundaries and of Ω-Al2Cu on dispersoids. This non-expected nanostructure for an alloy in T4 state was attributed to the heat that the plate experienced during the aircraft cycles. However, it is shown that this aging is reversible (after a solution treatment). Moreover, the very long time of outdoors exposure seems to have caused intergranular corrosion causing the early failure during tensile tests on some of the specimens. The artificial aging (low temperature, 100°C for up to 10,000h) applied on the modern 2017A alloy did not allow to reproduce the nanostructure of the old plate, meaning that isothermal conditions for artificial aging might not be appropriate in this case.
Effects of Si and Zr addition on strength and recrystallization behavior of Al-Mn alloy fin stocks for automotive heat exchanger
Authors: Shimosaka Daisuke , Ueno Mamoru
Published: November 2020

For an Al-Mn alloy heat exchanger fin stocks which continuous casting was simulated in, the effects of Si and Zr addition on strength and recrystallized grain structures after brazing heat treatment were investigated. As a result of tensile test, pre-brazed tensile strength was increased with increasing Si and Zr contents in the Al-Mn alloy. On the other hands, Zr addition have a small effect on post-brazed tensile strength regardless of Si contents. This was attributed the dissolution of Al3Zr or (Al,Si)3Zr precipitates during brazing heat treatment. Post-brazed grain structure were refined with increasing Si contents. Meanwhile, Zr addition led to larger post-brazed grain structures. It was found that Al3Zr or (Al,Si)3Zr precipitated during intermediate annealing played to major role in retarding recrystallization during brazing heat treatment.
INDUSTRIAL SEMISOLID CASTING PROCESS FOR SECONDARY ALUMINIUM ALLOYS FOR DECARBONISING LIGHTWEIGHT PARTS IN AUTOMOTIVE SECTOR
Authors: D’Errico Fabrizio , Casari Daniele , Alemani Mattia , Perricone Guido , Tosto Mauro
Published: November 2020

The life cycle holistic approach for the automotive sector highlighted how much important is working on decarbonisation of Al casting processes to produce vehicle components. Broadening the use of recycled aluminium alloys, instead of high energy intensive primary aluminium alloys, is key for environment preservation. While primary aluminium alloys are preferred by automotive original equipment manufacturers (OEMs) because impurities (mainly Fe) present in secondary aluminium alloys might cause fatigue properties decay, a new semisolid state process route has been developed at Brembo to drastically reduce the sensitivity of cast aluminium to Fe impurities. Based on these premises, during the CRAL European project in the framework of the LIFE Programme, an industrial prototype machinery - a vertical high pressure die casting machine - has been designed and constructed to inject secondary aluminium in the semisolid state. A number of A357 Fe-enriched brake callipers manufactured via the new process route have been fully investigated by fatigue tests, SEM and OM analyses in order to validate the new eco-sustainable product compared to conventional ones manufactured with primary aluminium by gravity casting.
Formation of bulk-laminated materials by localized deformation during ECAP of an AA6060 aluminum alloy
Authors: Wagner Martin Franz-Xaver , Frint Philipp
Published: November 2020

This paper addresses localized plastic flow during equal-channel angular pressing (ECAP) of an AA6060 aluminum alloy. We observe an alternating formation of shear bands and matrix bands during ECAP that leads to pronounced strain partitioning without cracking. Local deformation is analyzed by considering the distortion of indents along flow lines in the center of a split billet. We estimate equivalent strains of about 3.6 inside the shear bands, whereas plastic deformation in the adjacent matrix bands is almost negligible. Microstructural analysis by SEM and STEM confirms that the shear bands exhibit typical features of severely plastically deformed microstructures at the onset of forming an ultrafine-grained microstructure. We further present statistics of band widths, and we discuss the roles material hardening as well as ECAP die geometry (in terms of the inner die radius) in facilitating the recurrent localized deformation that, in the absence of crack nucleation, leads to the production of an interesting and novel type of bulk-laminated materials by ECAP.
Les myélinosomes : une nouvelle voie du contrôle de qualité des protéines
Authors: Marina Yefimova , Ravel Celia , Anne-Sophie Neyroud , Béré Emile , Bourmeyster Nicolas
Published: November 2020

Deux voies de dégradation des protéines mal repliées sont classiquement décrites : la voie du protéasome et la voie de l’autophagie. Nous décrivons ici une nouvelle voie de protéostase cellulaire ne dégradant pas la protéine anormale mais l’expulsant hors de la cellule grâce à des nanovésicules appelées myélinosomes. Ces myélinosomes sont produits par la cellule dans des situations pathologiques ou de stress en lien avec des facteurs génétiques ou environnementaux. Sur le plan morphologique, les myélinosomes sont caractérisés par des membranes osmiophiles denses aux électrons dont l’arrangement empilé est semblable à celui de la myéline et présente jusqu’à 30 feuillets selon le type de cellule. Dans deux modèles, au moins, de maladies génétiques (la maladie de Huntington et la mucoviscidose), les myélinosomes sont importants pour éliminer les protéines mutées par un processus sécrétoire inhabituel, évitant ainsi leur agrégation dans les cellules.
Une brève introduction à l’intelligence artificielle
Authors: Jean Aurélie
Published: November 2020

Depuis plus d’une décennie, l’intelligence artificielle (IA) vit une accélération dans son développement et son adoption. En médecine, elle intervient dans la recherche fondamentale et clinique, la pratique hospitalière, les examens médicaux, les soins ou encore la logistique. Ce qui contribue à l’affinement des diagnostics et des pronostics, à une médecine encore plus personnalisée et ciblée, à des avancées dans les technologies d’observations et d’analyses ou encore dans les outils d’interventions chirurgicales et autres robots d’assistance. De nombreux enjeux propres à l’IA et à la médecine, tels que la dématérialisation des données, le respect de la vie privée, l’explicabilité des algorithmes, la conception de systèmes d’IA inclusifs ou leur reproductibilité, sont à surmonter pour construire une confiance du corps hospitalier dans ces outils. Cela passe par une maîtrise des concepts fondamentaux que nous présentons ici
Krankenhausbetrieb in der Pandemie: Simulation ersetzt Bauchgefühl
Authors: Lang Michael
Published: November 2020

Das Krankenhaus Zams in Tirol hat mit einem Simulationstool getestet, wie sich der Krankenhausbetrieb vor einem Ansturm von Covid-19-Patienten besser planen und steuern lässt.
Acoustic tweezers find their biomedical niche
Authors: Fore Meredith
Published: November 2020

Longer wavelengths allow acoustic tweezers to manipulate larger biological samples, an appealing prospect to lab-on-a-chip developers.
Detection of femtosecond spin voltage pulses in a thin iron film
Authors: Bühlmann K. , Saerens G. , Vaterlaus A. , Acremann Y.
Published: November 2020

We present experimental evidence of a spin voltage—a difference between the chemical potentials of the two spin directions—in a thin iron film based on spin- and time-resolved photoemission spectroscopy. This voltage is the driving force for a spin current during the ultrafast demagnetization of the sample. The observed magnitude is on the order of 50 mV, a value that is quite consistent with predictions based on particle conservation and persists for approximately 100 fs.
Experimental demonstration of the wave attenuation capability of a piezoelectric metamaterial beam by using correlation for signal processing
Authors: Xu Jiawen , Zhang Xin , Yan Ruqiang
Published: November 2020

Piezoelectric metamaterials with inductance shunt circuits connected to the transducers have attractive potential for guiding and attenuating elastic waves. However, it is challenging to evaluate their wave attenuation capability experimentally because the signals of transmitted waves within the bandgap have extremely small amplitudes and are submerged in noise. The present paper reports a method for revealing the wave attenuation features of a piezoelectric metamaterial beam by taking advantage of the physical correlation between the excitation and the transmitted and incident waves. Correlations between the excitation and the measured waves are calculated in real time to eliminate noise. It is demonstrated that wave attenuation features within the bandgap can be recovered from noise with an amplitude that is 69.1 dB larger than that of the transmitted wave. The transmission diagram is presented, and wave attenuation of up to −50.7 dB can be observed. Also, the correlation-based signal processing procedure is effective for illustrating the resistance-load-based wave attenuation behavior of the piezoelectric metamaterial beam. This method can be extended to the experimental analysis of many other types of metamaterials and phononic crystals.
Bandgap modification of titanium dioxide doped with rare earth ions for luminescent processes
Authors: Reséndiz López Eder , Morales-Luna Michael , Vega González Marina , Aruna-Devi R. , de Moure-Flores Francisco , Mayen Hernández Sandra. A. , Santos Cruz José
Published: November 2020

Yttrium oxide nanostructures doped with erbium and ytterbium ions were incorporated into a titanium dioxide (TiO2) host by a hydrothermal method to modify the bandgap of TiO2. The samples were prepared with different concentrations of nanophosphors (Y2O3: Er3+-Yb3+). Then, the samples were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), x-ray photoelectron spectroscopy (XPS), and photoluminescence spectroscopy. The XRD analysis revealed the mixture of anatase and rutile crystal structures for all the samples. The TEM measurements showed agglomerated particles with a spherical shape of around 50 nm. TiO2 doped with a high concentration of Y2O3:Er3+-Yb3+ exhibited a strong visible upconversion luminescence under the excitation of 980 nm (infrared laser) as compared to other samples. Photoluminescence studies revealed the green (522 nm), yellow (563 nm), and red emissions (661 nm) corresponding to 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 transitions of Er3+ in Y2O3:Er3+-Yb3+@TiO2 nanophosphors, respectively. Furthermore, DRS and XPS analyses revealed that Y2O3:Er3+-Yb3+ modified the bandgap of the TiO2 host.
Machine-learning predictions of polymer properties with Polymer Genome
Authors: Doan Tran Huan , Kim Chiho , Chen Lihua , Chandrasekaran Anand , Batra Rohit , Venkatram Shruti , Kamal Deepak , Lightstone Jordan P. , Gurnani Rishi , Shetty Pranav , Ramprasad Manav , Laws Julia , Shelton Madeline , Ramprasad Rampi
Published: November 2020

Polymer Genome is a web-based machine-learning capability to perform near-instantaneous predictions of a variety of polymer properties. The prediction models are trained on (and interpolate between) an underlying database of polymers and their properties obtained from first principles computations and experimental measurements. In this contribution, we first provide an overview of some of the critical technical aspects of Polymer Genome, including polymer data curation, representation, learning algorithms, and prediction model usage. Then, we provide a series of pedagogical examples to demonstrate how Polymer Genome can be used to predict dozens of polymer properties, appropriate for a range of applications. This contribution is closed with a discussion on the remaining challenges and possible future directions.
Two-temperature warm dense hydrogen as a test of quantum protons driven by orbital-free density functional theory electronic forces
Authors: Kang Dongdong , Luo Kai , Runge Keith , Trickey S. B.
Published: November 2020

We consider a steady-state (but transient) situation in which a warm dense aggregate is a two-temperature system with equilibrium electrons at temperature Te, ions at Ti, and Te ≠ Ti. Such states are achievable by pump–probe experiments. For warm dense hydrogen in such a two-temperature situation, we investigate nuclear quantum effects (NQEs) on structure and thermodynamic properties, thereby delineating the limitations of ordinary ab initio molecular dynamics. We use path integral molecular dynamics (PIMD) simulations driven by orbital-free density functional theory (OFDFT) calculations with state-of-the-art noninteracting free-energy and exchange-correlation functionals for the explicit temperature dependence. We calibrate the OFDFT calculations against conventional (explicit orbitals) Kohn–Sham DFT. We find that when the ratio of the ionic thermal de Broglie wavelength to the mean interionic distance is larger than about 0.30, the ionic radial distribution function is meaningfully affected by the inclusion of NQEs. Moreover, NQEs induce a substantial increase in both the ionic and electronic pressures. This confirms the importance of NQEs for highly accurate equation-of-state data on highly driven hydrogen. For Te > 20 kK, increasing Te in the warm dense hydrogen has slight effects on the ionic radial distribution function and equation of state in the range of densities considered. In addition, we confirm that compared with thermostatted ring-polymer molecular dynamics, the primitive PIMD algorithm overestimates electronic pressures, a consequence of the overly localized ionic description from the primitive scheme.
The relationships between land use and amphibian assemblages in a traditional agricultural area, the Sun Moon Lake, of Taiwan
Authors: Jung Chau-Ren , Wu Sheng-Hai
Published: November 2020

Abstract
ContextUnderstanding the relationships between land use and anuran habitat selection would help make conservation-management and habitat-restoration decisions. However, only a few studies have investigated all the available amphibian habitats in terrestrial and aquatic environments.
AimsThe objective of the present study is to assess the associations between different land-use types and individual anuran species in a traditional agricultural area. We also hypothesise that connectivity and land-use heterogeneity are important in determining species richness.
MethodsWe conducted monthly roadside calling surveys at 71 sites in the Sun Moon Lake (SML) region in central Taiwan during 2008–2010. Non-metric multidimensional scaling (NMDS) with envfit was used to investigate the relationships between land-use characteristics and anuran assemblage. We use a site-occupancy model to assess the associations between land use and occupancy rate of each species. Generalised linear regression with Poisson distribution was used to assess the relationships among connectivity, land-use heterogeneity and species richness.
Key resultsIn total, 19 species in five families were detected by roadside calling surveys. The NMDS results showed anuran assemblages in the SML region being distributed through an environmental gradient from those most dominated by agricultural land to forest-dominant sites. According to site-occupancy models, the occupancy rates of anurans were mainly correlated with proportion of agricultural land, grassland and distance to river. The species richness was positively correlated with land-use heterogeneity.
ConclusionsThe results showed that the distributions of anurans largely depended on surrounding land-use types in the terrestrial environment. The major trend of anuran assemblages in the traditional agricultural area was dependent on the transition from forest to agricultural land.
ImplicationsThe data suggested that land-use heterogeneity should be a primary consideration for increasing amphibian species richness.
The classroom as a space of welcome: exploration of the current challenges of teaching Spanish for refugees (El aula como espacio de acogida: exploración de los desafíos actuales sobre la enseñanza de español para personas refugiadas)
Authors: Tomás-Cámara Dulcinea
Published: November 2020

The scant examination and dearth of academic and didactic contributions in Spain of teaching–learning Spanish for refugees is a clear shortcoming which should begin to be rectified within the next few years given the increasing presence of applicants and beneficiaries of international protection (henceforth ABIP) in our country. Given this dearth, and based on our experience as teachers with this student group, this study aims to offer several particularly illustrative examples of this phenomenon of structural divergence in language learning, in particular in relation to the crises of meaning that refugees deploy on traditional didactic materials, which reveal profound imbalances and shortcomings when faced with unprecedented pedagogical expectations. Here, it is also worth noting that a class of this kind — as a locus of (re)inscription of meanings — takes on additional functions not included in common pedagogical practice which stem from a profoundly novel educational context. To conclude, we seek to outline several reflections and recommendations which can stimulate proposed practices to help teachers, volunteers or technical staff deal with this contemporary social, political and educational challenge.
Key comparison CCQM-K18.2016: pH of carbonate buffer
Authors: Waters Jason F , Máriássy Michal , Bastkowski Frank , Asakai Toshiaki , Prokunin Sergey V , Gonzaga Fabiano B , Dimitrova Lyudmila , Amaya Ronald C , Quezada Henry T , Vospelova Alena , Rozikova Matilda , Snedden Alan , Stoica Daniela , Sander Beatrice , Jakusovszky Beáta , Maksimov Igor , Onuma Sachiko , Suzuki Toshihiro , Ruiz Jazmin M , Ortiz-Aparicio José L , Tincona Galia , Vasquez Javier , Pawlina Monika , Kozlowski Wladyslaw , Dobrovolskiy Vladimir I , Aprelev Alexey V , Hanková Zuzana , Rodruangthum Patumporn , Uysal Emrah , Liv Lokman , Nakiboglu Nuri , Gavrilkin Vladimir , Petrenko Anton , Manska Oleksandra , Easley Regina A , Fajardo Simone
Published: November 2020

Key comparison (KC) CCQM-K18.2016 was performed to evaluate the degree of equivalence between pH measurement results on an unknown carbonate buffer reported by participating National Metrology Institutes and Designated Institutes (NMI/DIs). The participants used the highest metrological method existing at their institution. The nominal buffer pH was 10.0 and was determined only at 25 °C. Good agreement of the results is demonstrated by most participants.

Main text

To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.

The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
A modified practical homodyne detector model for continuous-variable quantum key distribution: detailed security analysis and improvement by the phase-sensitive amplifier
Authors: Huang Yundi , Zhang Yichen , Xu Bingjie , Huang Luyu , Yu Song
Published: November 2020

The practical homodyne detector model of continuous-variable quantum key distribution models the inherent imperfections of the practical homodyne detector, namely the limited detection efficiency and the electronic noise, into trusted loss. However, the conventional practical homodyne detector model is valid only when both the imperfections of the practical homodyne detector are calibrated. In this paper, we show a modified practical homodyne detector model that can model the imperfections separately. The phase-sensitive amplifier (PSA) is further applied to compensate the imperfections of the practical homodyne detector. The feasibility of the modified practical homodyne detector model with the PSA is proved and the security analysis is provided in detail. Simulation results reveal that the PSA can be used to improve the performance of the modified practical homodyne detector model, and when the gain is infinitely high, the limited detection efficiency can be fully compensated.
Ultra-high-resolution optical absorption spectroscopy of DC plasmas at low pressure using a supercontinuum laser combined with a laser line tunable filter and a HyperFine spectrometer
Authors: Durocher-Jean Antoine , Jean-Ruel Hubert , Dion-Bertrand Laura-Isabelle , Blais-Ouellette Sébastien , Stafford Luc
Published: November 2020

Optical absorption spectroscopy of non-equilibrium plasmas using a supercontinuum laser combined with a laser line tunable filter and a HyperFine spectrometer is examined. Owing to the <2 pm spectral resolution of the HyperFine system, details on the absorption line intensity, position and width can be obtained with very high precision using a broadband light emission source. As an example, absorption spectroscopy measurements were recorded in a reduced-pressure, nominally pure argon DC plasma column and allowed for the determination of the neutral gas temperature and the Ar 1s2 and Ar 1s4 (Paschen notation) number densities. At a pressure of 1 Torr, a discharge current of 20 mA, and an absorption length of 18 cm, the analysis of the Ar 2p3-1s2 and Ar 2p8-1s4 absorption lines at respectively 840.8 nm and 842.5 nm resulted in number densities of

n

1

s
2

=

5.5

×

1015 m−3 and

n

1

s
4

=

1.1

×

1016 m−3 and a neutral gas temperature of T
g = 340 K. These values are typical of DC discharges operated under similar experimental conditions. While the fractional absorption of both lines decreased with decreasing optical absorption path, the number densities remained the same, as expected. Finally, the number densities increased with increasing discharge current, a result also coherent with the literature.
A first-principles comparative study of lithium, sodium, potassium and calcium storage in two-dimensional Mg2C
Authors: Chu Y Z , Yeoh K H , Chew K-H
Published: November 2020

Two-dimensional (2D) materials have recently emerged as potential candidates for high-capacity lithium-ion batteries anode materials because of their compelling physicochemical and structural properties. In the present study, we use first-principles calculations to investigate the performance of 2D Mg2C as anode materials for Li, Na, K and Ca-ions batteries. The calculated average open-circuit voltage are 0.37, 0.50, 0.03 and 0.06 eV vs Li, Na, K, Ca. No significant structural deformations are observed on the 2D Mg2C upon the adsorption of Li, Na, K or Ca and the metallic characteristic of the 2D Mg2C is retained. The metallic behaviour of both pristine and adsorbed Mg2C ensures the desirable electric conductivity, implying the advantages of 2D Mg2C for batteries. The Na and K atoms show an extremely high diffusivity on the 2D Mg2C with a low energy barrier of 0.08 and 0.04 eV respectively, which is about an order of magnitude smaller than that of Li atom. For the Na and K atoms, the theoretical storage capacity can reach up to 1770 mAh g−1, nearly two times that of the Li atom of 885 mAh g−1. Our study suggests that the 2D Mg2C is a promising anode material which offers a fast ion diffusion and high storage capacity.
Effect of an inhomogeneous electron density profile on the transmission microwave frequency spectrum of the cutoff probe
Authors: Kim S J , Lee J J , Lee Y S , Kim D W , You S J
Published: November 2020

The cutoff probe (CP), which precisely measures electron density from a microwave transmission (S
21) spectrum, has been successfully developed through physical models under the assumption of homogeneous plasma between the probe tips. In practice, however, the chamber and sheath structure, flow effects, and the probe insertion itself produce plasma inhomogeneity between the probe tips, which necessitates the study of any related effects on the CP measurement results. This paper investigated the effect of inhomogeneous plasma on the S
21 of the CP through a three-dimensional E/M wave simulation with various density gradient directions. The simulations found, notably, double cutoff peaks and a cutoff frequency shift in the S
21 that depend on the gradient direction. These results are analyzed via a simple circuit model of the CP, and their origins are elucidated at the end of this paper.
Unipolar arc plasmas on nanostructured tungsten surfaces under perpendicular magnetic field
Authors: Hwangbo Dogyun , Nishijima Daisuke , Kajita Shin , Doerner Russell P , Ohno Noriyasu
Published: November 2020

Unipolar arcing is an important phenomenon in terms of wall erosion and the subsequent plasma contamination in nuclear fusion devices. In this study, unipolar arc plasmas are experimentally explored under the presence of the external magnetic field perpendicular to a tungsten (W) sample on which a ‘fuzz’ nanostructure surface is formed. It is found that the fuzz layer thickness, d
fuzz, plays a dominant role in determining the motion of arc spots, the arc ignition probability, and arc plasma parameters. High-speed imaging reveals that the motion of arc spots becomes more collective, as d
fuzz increases. Interestingly, arc spots make a circle while moving outward. With increasing d
fuzz, the amount of eroded W atoms increases, as indicated from an observed increase in the total visible emission intensity, while the arc ignition probability is found to drop. The physical mechanisms are discussed, in detail, based on spectroscopic measurements of the electron temperature, obtained from Boltzmann plots of both W I and W II, and the electron density, determined from Stark broadening of W I lines.
Evaluation of Cd1–x
Zn
x
S as electron transport layer in superstrate and inverted configurations of Sb2Se3 solar cells with n-i-p structure
Authors: Ayala-Mató F , Vigil-Galán O , Seuret-Jiménez D , Courel Maykel , Fernández Susana
Published: November 2020

In this work, we evaluate the role of the ternary compound, Cd1–x
Zn
x
S, as an electron-transport layer (ETL) in the n-i-p structure of antimony selenide (Sb2Se3) solar cells. The incorporation of Zn reduces the amount of Cd and contributes to improving the power-conversion efficiency of the solar cell. On the other hand, the n-i-p structure makes it possible to overcome two issues that impair the efficiency of Sb2Se3 solar cells: the potential barrier due to the rear contact and the low hole concentration in the Sb2Se3 absorber material. In this paper, we present a theoretical work on Sb2Se3 solar cells using the SCAPS 1-D software. The theoretical analysis allows us to understand the impact of the semiconductor parameters on efficiency and also to find the optimal values for an optimized device. The optimal molar composition of the ternary compound is investigated in the superstrate and inverted configurations. Parameters such as the thickness, defect density, and the acceptor concentration of the Cd1–x
Zn
x
S and Sb2Se3 layers are optimized. Also, we analyze the impact of interface-defect density at the hole-transport layer (HTL) (Sb2Se3) and the ETL (Sb2Se3). Following optimization, a power-conversion efficiency (η) of 14.29% is obtained using Cd0.4Zn0.6S as the ETL and Cu2O as the HTL in the superstrate configuration. This simulation process is expected to guide other experimentalists in the design and manufacture of solar cells.
Influence of uniform momentum zones on frictional drag within the turbulent boundary layer*
Authors: Wang Kangjun , Jiang Nan
Published: November 2020

Based on a set of experimental databases of turbulent boundary layers obtained from particle image velocimetry in the streamwise-wall-normal plane at friction-velocity-based Reynolds number Reτ
= 612, the influence of uniform momentum zones (UMZs) on the skin-friction drag is investigated. The skin-friction drag is measured by the single-pixel ensemble correlation method. The results show that the velocity fields with the number of UMZs larger than the mean value have a relatively low skin-friction drag, while the velocity fields with the number of UMZs less than the mean value have a relatively high skin-friction drag. By analyzing the statistical characteristics of UMZs, the dynamic correlation between the UMZs and skin-friction drag is explored. The velocity fields with a low number of UMZs present a sweep event. These sweep motions intensify the small-scale Reynolds shear stress in the near-wall region by modulation effects. The enhancement of small-scale Reynolds shear stress is the direct reason for the high skin-friction drag. Increasing the proportion of velocity fields with high UMZs amount may be a direction to reduce the skin-friction drag within the TBL.
Raman scattering from highly-stressed anvil diamond*
Authors: Liu Shan , Tang Qiqi , Wu Binbin , Zhang Feng , Liu Jingyi , Fan Chunmei , Lei Li
Published: November 2020

The high-frequency edge of the first-order Raman mode of diamond reflects the stress state at the culet of anvil, and is often used for the pressure calibration in diamond anvil cell (DAC) experiments. Here we point out that the high-frequency edge of the diamond Raman phonon corresponds to the Brillouin zone (BZ) center Γ point as a function of pressure. The diamond Raman pressure gauge relies on the stability of crystal lattice of diamond under high stress. Upon the diamond anvil occurs failure under the uniaxial stress (197 GPa), the loss of intensity of the first-order Raman phonon and a stress-dependent broad Raman band centered at 600 cm−1 are observed, which is associated with a strain-induced local mode corresponding to the BZ edge phonon of the L
1 transverse acoustic phonon branch.
Effects of Nb and Mo additions on thermal behavior, microstructure and magnetic property of FeCoZrBGe alloy*
Authors: Sun Yaming , Wang Zhiqun , Xu Shi-Chong , Hua Zhong
Published: November 2020

Both Nb and Mo additions play a vital role in FeCo-based alloys and it is crucial to understand their roles and contents on thermal behavior, microstructural feature and magnetic property of alloys. Nanocrystalline alloy ribbons Fe40Co40Zr9 – y
M
y
B10Ge1 (y = 0–4; M = Nb, Mo) were prepared by crystallizing the as-quenched amorphous alloys. The effects of Nb and Mo additions on structures and properties of the Fe40Co40Zr9B10Ge1 alloy are investigated systemically and compared. With increasing Nb or Mo content, the primary crystallization temperature, grain size of α-Fe(Co) phase and coercivity H
c all decrease. Moreover, the effect of Mo addition on thermal behavior, microstructure and magnetic properties of the FeCoZrBGe alloy is greater compared to Nb addition. The gap between primary and secondary crystallization peaks of Mo-containing alloys is wider than that of Nb-containing alloys. Both grain size and H
c of Mo-containing alloys are smaller than those of Nb-containing alloys. For Fe40Co40Zr9B10Ge1 alloy, high Mo addition proportion is better compared to high Nb addition proportion.
High-resolution bone microstructure imaging based on ultrasonic frequency-domain full-waveform inversion*
Authors: Li Yifang , Shi Qinzhen , Li Ying , Song Xiaojun , Liu Chengcheng , Ta Dean , Wang Weiqi
Published: November 2020

The main challenge in bone ultrasound imaging is the large acoustic impedance contrast and sound velocity differences between the bone and surrounding soft tissue. It is difficult for conventional pulse-echo modalities to give accurate ultrasound images for irregular bone boundaries and microstructures using uniform sound velocity assumption rather than getting a prior knowledge of sound speed. To overcome these limitations, this paper proposed a frequency-domain full-waveform inversion (FDFWI) algorithm for bone quantitative imaging utilizing ultrasonic computed tomography (USCT). The forward model was calculated in the frequency domain by solving the full-wave equation. The inverse problem was solved iteratively from low to high discrete frequency components via minimizing a cost function between the modeled and measured data. A quasi-Newton method called the limited-memory Broyden–Fletcher–Goldfarb–Shanno algorithm (L-BFGS) was utilized in the optimization process. Then, bone images were obtained based on the estimation of the velocity and density. The performance of the proposed method was verified by numerical examples, from tubular bone phantom to single distal fibula model, and finally with a distal tibia-fibula pair model. Compared with the high-resolution peripheral quantitative computed tomography (HR-pQCT), the proposed FDFWI can also clearly and accurately presented the wavelength scaled pores and trabeculae in bone images. The results proved that the FDFWI is capable of reconstructing high-resolution ultrasound bone images with sub-millimeter resolution. The parametric bone images may have the potential for the diagnosis of bone disease.
Density wave and topological superconductivity in the magic-angle-twisted bilayer-graphene*
Authors: Zhang Ming , Zhang Yu , Lu Chen , Chen Wei-Qiang , Yang Fan
Published: November 2020

The model dependence in the study of the magic-angle twisted bilayer-graphene (MA-TBG) is an important issue in the research area. It has been argued previously that the two-band tight-binding (TB) model (per spin and valley) cannot serve as a start point for succeeding studies as it cannot correctly describe the topological aspect of the continuum-theory model near the Dirac nodes in the mini Brillouin zone (MBZ). For this purpose, we adopt the faithful TB model [Phys. Rev. B
99 195455 (2019)] with five bands (per spin and valley) as our start point, which is further equipped with extended Hubbard interactions. Then after systematic random-phase-approximation (RPA) based calculations, we study the electron instabilities of this model, including the density wave (DW) and superconductivity (SC), near the van Hove singularity (VHS). Our results are as follows. In the case neglecting the tiny inter-valley exchange interaction, the exact SU(2)K × SU(2)K′ symmetry leads to the degeneracy between the inter-valley charge DW (CDW) and the spin DW (SDW) (which would be mixed then), and that between the singlet d + id-wave and triplet p + ip-wave topological SCs. When a realistic tiny inter-valley exchange interaction is turned on with nonzero coefficient (J
H ≠ 0), the SDW or CDW is favored respectively at the critical point, determined by J
H → 0− or J
H → 0+. In the mean time, the degeneracy between the singlet d + id-wave and triplet p + ip-wave topological SCs is also lifted up by the tiny J
H. These results are highly similar to the results of our previous study [arXiv:2003.09513] adopting the two-band TB model, with the reason lying in that both models share the same symmetry and Fermi-surface (FS) nesting character near the VHS. Such a similarity suggests that the low-energy physics of the doped MA-TBG is mainly determined by the symmetry and the shape of the FS of the doped system, and is insensitive to other details of the band structure, including the topological aspects near the Dirac nodes in the MBZ.
Progress on band structure engineering of twisted bilayer and two-dimensional moiré heterostructures*
Authors: Yao Wei , Aeschlimann Martin , Zhou Shuyun
Published: November 2020

Artificially constructed van der Waals heterostructures (vdWHs) provide an ideal platform for realizing emerging quantum phenomena in condensed matter physics. Two methods for building vdWHs have been developed: stacking two-dimensional (2D) materials into a bilayer structure with different lattice constants, or with different orientations. The interlayer coupling stemming from commensurate or incommensurate superlattice pattern plays an important role in vdWHs for modulating the band structures and generating new electronic states. In this article, we review a series of novel quantum states discovered in two model vdWH systems — graphene/hexagonal boron nitride (hBN) hetero-bilayer and twisted bilayer graphene (tBLG), and discuss how the electronic structures are modified by such stacking and twisting. We also provide perspectives for future studies on hetero-bilayer materials, from which an expansion of 2D material phase library is expected.
Network-based brain–computer interfaces: principles and applications
Authors: Gonzalez-Astudillo Juliana , Cattai Tiziana , Bassignana Giulia , Corsi Marie-Constance , De Vico Fallani Fabrizio
Published: November 2020

Brain–computer interfaces (BCIs) make possible to interact with the external environment by decoding the mental intention of individuals. BCIs can therefore be used to address basic neuroscience questions but also to unlock a variety of applications from exoskeleton control to neurofeedback rehabilitation. In general, BCI usability depends on the ability to comprehensively characterize brain functioning and correctly identify the user’s mental state. To this end, much of the efforts have focused on improving the classification algorithms taking into account localized brain activities as input features. Despite considerable improvement BCI performance is still unstable and, as a matter of fact, current features represent oversimplified descriptors of brain functioning. In the last decade, growing evidence has shown that the brain works as a networked system composed of multiple specialized and spatially distributed areas that dynamically integrate information. While more complex, looking at how remote brain regions functionally interact represents a grounded alternative to better describe brain functioning. Thanks to recent advances in network science, i.e. a modern field that draws on graph theory, statistical mechanics, data mining and inferential modeling, scientists have now powerful means to characterize complex brain networks derived from neuroimaging data. Notably, summary features can be extracted from brain networks to quantitatively measure specific organizational properties across a variety of topological scales. In this topical review, we aim to provide the state-of-the-art supporting the development of a network theoretic approach as a promising tool for understanding BCIs and improve usability.
Multi-dimensional persistent feature analysis identifies connectivity patterns of resting-state brain networks in Alzheimer’s disease
Authors: Li Jin , Bian Chenyuan , Luo Haoran , Chen Dandan , Cao Luolong , Liang Hong
Published: November 2020

Objective. The characterization of functional brain network is crucial to understanding the neural mechanisms associated with Alzheimer’s disease (AD) and mild cognitive impairment (MCI). Some studies have shown that graph theoretical analysis could reveal changes of the disease-related brain networks by thresholding edge weights. But the choice of threshold depends on ambiguous cognitive conditions, which leads to the lack of interpretability. Recently, persistent homology (PH) was proposed to record the persistence of topological features of networks across every possible thresholds, reporting a higher sensitivity than graph theoretical features in detecting network-level biomarkers of AD. However, most research on PH focused on zero-dimensional features (persistence of connected components) reflecting the intrinsic topology of the brain network, rather than one-dimensional features (persistence of cycles) with an interesting neurobiological communication pattern. Our aim is to explore the multi-dimensional persistent features of brain networks in the AD and MCI patients, and further to capture valuable brain connectivity patterns. Approach. We characterized the change rate of the connected component numbers across graph filtration using the functional derivative curves, and examined the persistence landscapes that vectorize the persistence of cycle structures. After that, the multi-dimensional persistent features were validated in disease identification using a K-nearest neighbor algorithm. Furthermore, a connectivity pattern mining framework was designed to capture the disease-specific brain structures. Main results. We found that the multi-dimensional persistent features can identify statistical group differences, quantify subject-level distances, and yield disease-specific connectivity patterns. Relatively high classification accuracies were received when compared with graph theoretical features. Significance. This work represents a conceptual bridge linking complex brain network analysis and computational topology. Our results can be beneficial for providing a complementary objective opinion to the clinical diagnosis of neurodegenerative diseases.
Experimental studies of plasma-antenna coupling with the JET Alfvén Eigenmode Active Diagnostic
Authors: Tinguely R.A. , Puglia P.G. , Fil N. , Dowson S. , Porkolab M. , Dvornova A. , Fasoli A. , Fitzgerald M. , Guillemot V. , Huysmans G.T.A. , Maslov M. , Sharapov S. , Testa D. , contributors JET
Published: November 2020

This paper presents a dedicated study of plasma-antenna (PA) coupling with the Alfvén Eigenmode Active Diagnostic (AEAD) in JET. Stable AEs and their resonant frequencies f, damping rates γ < 0, and toroidal mode numbers n are measured for various PA separations and limiter versus X-point magnetic configurations. Two stable AEs are observed to be resonantly excited at distinct low and high frequencies in limiter plasmas. The values of f and n do not vary with PA separation. However, |γ| increases with PA separation for the low-f, but not high-f, mode, yet this may be due to slightly different edge conditions. The high-f AE is detected throughout the transition from limiter to X-point configuration, though its damping rate increases; the low-f mode, on the other hand, becomes unidentifiable. The linear, resistive MHD code CASTOR is used to simulate the frequency scan of an AEAD-like external antenna. For the limiter pulses, the high-f mode is determined to be an n = 0 GAE, while the low-f mode is likely an n = 2 TAE. During the transition from limiter to X-point configuration, CASTOR indicates that n = 1 and 2 EAEs are excited in the edge gap. These results extend previous experimental studies in JET and Alcator C-Mod; validate the computational work performed by Dvornova et al (2020 Phys. Plasmas
27 012507); and provide guidance for the optimization of PA coupling in upcoming JET energetic particle experiments, for which the AEAD will aim to identify the contribution of alpha particles to AE drive during the DT campaign.
Structural and Morphological Properties of Undoped and Manganese Doped Hematite Nanoparticles Prepared by Ball Milling Method
Authors: Hadianto Heri , Amiruddin Erwin , Venera Rebi Septiawan Putri , Aprilia Vivi
Published: November 2020

Hematite nanoparticles of undoped and manganese doped were synthesized from natural sand of Logas District Kuansing Regency Riau Province by ball milling method. Structural and morphological properties of these compounds were studied using X-Ray Diffractometer (XRD) and Scanning electron microscope (SEM) respectively. Crystalline structure, lattice parameters, morphologies of the synthesized compounds were studied and the results are discussed. X-ray diffraction (XRD) confirmed the presence of a hematite (α-Fe2O3) phase. Average crystallite size based on flections (1 0 4) for undoped and manganese doped magnetic iron oxide particles are 39.2 nm and 38.2 respectively. The intensity of (1 0 4) reflection is stronger for magnetic iron oxide synthesized for 60 hours than that of 2 step (60+60) hours ball milling. This indicates the product grown along (1 0 4) direction. The average crystallite size decreases when magnetic iron oxide is doped with 10% Mn as confirmed by SEM images.
Effect of Vegetation Profile and Air Data Rate on Packet Loss Performance of LoRa E32-30dBm 433 MHz as a Wireless Data Transmission
Authors: Wiyadi Eri , Setiadi Rahmondia Nanda , Umar Lazuardi
Published: November 2020

Internet of Things (IoT) communication network is currently one of the rapidly expanding uses a technology called the Long Range (LoRa) module using unlicensed industrial, scientific, and medical (ISM) radio frequencies. For sensor data transmission, the propagation depends on many parameters, such as transmit power, antenna, and vegetation obstacles on the propagation path. This work presents a 30 dBm LoRa E32-433T30D module of 433 MHz used for biosensor data transmission. LoRa performance testing was carried out in obstacle-dense areas (NLoS) of the Tempuling forest Riau that varies the distance parameters, and the programmable transmission speed (ADR) ranges from 1.2 Kbps to 9.2 Kbps. Results show that the higher the ADR value, the shorter the signal range, which is represented by the increase of the packet loss number. The highest ADR value is 19.2 Kbps signal coverage is only able to cover a distance of 1.4 Km with a data loss number of 86 %, while for 1.2 Kbps experiences a data loss of 20 % at a distance of 2 Km. The highest signal strength RSSI value was obtained at -67 dBm at a distance of 200 m and the lowest at -102 dBm at a distance of 2 Km. The decrease in RSSI value is caused by attenuation and signal interference from the obstacle height that exceeds the height of the antenna.
Preparation of Iron Oxide Magnetic Nanoparticles Natural Sand of Rokan River Synthesis with Ball Milling
Authors: Salomo S. , Erwin A. , Usman M. , Muhammad H. , Nita Y. , Linda W.
Published: November 2020

Natural sand samples taken from the Rokan river, Riau Province, Indonesia, have been ball milled for 100 (one hundred) hours using a ball with a diameter of 1.5 cm and a constant rotation angular velocity of the tube of 100 revolutions / minute. Neodymium Iron Boron (NdFeB) strong magnets are used to separate magnetic minerals from their non-magnetic minerals. Magnetic induction was measured using the Pasco PS-2162 probe and its value was used to calculate the magnitude of magnetic susceptibility, it turns out that the magnetic susceptibility value of the 100-hour Ball Milling results increased significantly when compared to the magnetic susceptibility before Ball Milling, 968,245x 10−5 becomes 19.471x 10−5. The results of the X-Ray Fluorescence (XRF) test showed that the percentage of Fe milled increased from 1.669% to 35.187%, the particle size obtained from the scanning electron microscope (SEM) results was in the nanometer order of 78 nm and the X-Ray Difractometer (XRD) results.) shows that the magnetic nanoparticles produced are dominated by the hematite phase (α-Fe2O3) and the others are in the magnetite (Fe3O4) phase..