bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-motion and heterogeneous droplet dynamics in moderately attractive dense emulsions
Authors: Kim Ha Seong , Xu Yixuan , Scheffold Frank , Mason Thomas G
Published: January 2021

We show that diffusing wave spectroscopy (DWS) is sensitive to the presence of a moderate short-range attraction between droplets in uniform fractionated colloidal emulsions near and below the jamming point associated with monodisperse hard spheres. This moderate interdroplet attraction, induced by micellar depletion, has an energy of about ∼2.4 k
B
T, only somewhat larger than thermal energy. Although changes in the mean free path of optical transport caused by this moderate depletion attraction are small, DWS clearly reveals an additional secondary decay-to-plateau in the intensity autocorrelation function at long times that is not present when droplet interactions are nearly hard. We hypothesize that this secondary decay-to-plateau does not reflect the average self-motion of individual droplets experiencing Brownian excitations, but instead results from heterogeneous dynamics involving a sub-population of droplets that still experience bound motion yet with significantly larger displacements than the average. By effectively removing the contribution of this secondary decay-to-plateau, which is linked to greater local heterogeneity in droplet structure caused by the moderate attraction, we obtain self-motion mean square displacements (MSDs) of droplets that reflect only the initial primary decay-to-plateau. Moreover, we show that droplet self-motion primary plateau MSDs can be interpreted using the generalized Stokes-Einstein relation of passive microrheology, yielding quantitative agreement with plateau elastic shear moduli measured mechanically.
A new technique for real-time measurements of potassium and sodium aerosols based on field-reversal surface ionization
Authors: Gall Dan , Nejman Charlotta , Allguren Thomas , Andersson Klas , Pettersson Jan B C
Published: January 2021

A new method for real-time measurements of potassium and sodium containing aerosol particles is described and verified. The method is based on surface ionization technique and may be used to explore the alkali chemistry related to high temperature chemistry processes. The measurement device is a further development of the simple and cost-effective surface ionization detector previously used for online alkali measurements in combustion and gasification research. The discrimination between sodium and potassium is possible due to differences in their surface desorption kinetics and facilitated by rapidly reversing the field potential between the ion source and the nearby collector. The instrument is evaluated in a series of laboratory experiments using size-selected alkali salt particles containing KCl, NaCl, K2SO4, Na2SO4, KNO3 and NaNO3. The filament temperature was found to be a key influencing factor in order to optimize the strength and Na–K deviation of the observed ion current. The ability to simultaneously report absolute concentrations of Na and K makes the instrument attractive for solid fuel conversion of alkali-rich fuels such as low-grade biomass and to explore behavior deviations of Na and K in high temperature processes.
Phenomenological model of thermal transport in carbon nanotube and hetero-nanotube films
Authors: Wang Pengyingkai , Feng Ya , Xiang Rong , Inoue Taiki , Anisimov Anton , Kauppinen Esko I , Chiashi Shohei , Maruyama Shigeo
Published: January 2021

The thermal properties of individual single-walled carbon nanotubes (SWCNTs) have been well documented in the literature following decades of intensive study. However, when SWCNTs form a macroscale assembly, the thermal transport in these complex structures usually not only depends on the properties of the individual tubes, but also is affected and sometimes dominated by inner structural details, e.g. bundles and junctions. In this work, we first performed an experimental measurement of the thermal conductivities of individual SWCNT bundles of different sizes using a suspended micro-thermometer. The results, together with the data that we obtained from a previous work, give a complete experimental understanding of the effect of bundling on the thermal conductivity of SWCNTs. With these quantitative understandings, we propose a phenomenological model to describe the thermal transport in two-dimensional (2D) SWCNT films. The term ‘line density’ is defined to describe the effective thermal transport channels in this complex 2D network. Along with experimentally obtained geometric statistics and film transparency, the thermal conductance of SWCNTs is estimated, and the effects of bundle length, diameter, and contact conductance are systematically discussed. Finally, we extend this model to explain thermal transport in 2D networks of one-dimensional van der Waals heterostructures, which are coaxial hetero-nanotubes we recently synthesized using SWCNTs as the template. This extended model suggests that the contribution of boron nitride nanotubes (BNNTs) to the overall performance of a SWCNT–BNNT heterostructured film depends on the transparency of the original SWCNT film. The increase in the thermal conductance of a highly transparent film is estimated to be larger than that of a less transparent film, which shows a good agreement with our experimental observations and proves the validity of the proposed phenomenological model.
Generation of astrophysics-relevant helical magnetic structures in laser-produced plasma
Authors: Tao Tao , Zhao Bin , Zheng Jian
Published: January 2021

Helical magnetic fields play an important role in star formation and stellar wind shaping. In recent years, there have been many experiments using pure poloidal or toroidal fields to confine hot plasma species that have successfully reproduced jets and instability patterns similar to those in the universe, but the role of helical magnetic structures is rarely explored due to the complexity of their generation. However, certain processes like cloud angular momentum extraction will only manifest in helical field configurations. In this article, we propose and numerically illustrate a method that can generate helical magnetic structures inside the plasma by merging a self-generated toroidal field and an externally applied poloidal field. The resulting helical field is dynamically important regarding pressure, adjustable in strength and pitch angle, and consistent with the actual astrophysical outflow in terms of boundary conditions. This method shows how to integrate a helical field structure into laser-plasma experiments, and it provides a framework for future studies on stellar outflow interaction with their embedded helical fields.
Experimental confirmation of solvated electron concentration and penetration scaling at a plasma–liquid interface
Authors: Martin Daniel C , Bartels David M , Rumbach Paul , Go David B
Published: January 2021

In this work, the transport of the plasma injected solvated electron is experimentally studied using total internal reflection absorption spectroscopy (TIRAS). A recently derived a theoretical model predicts power-law scalings between the interfacial concentration n
0 and penetration depth l with plasma current density j, namely

n

0

∝

j

e

(

2

3

)

and

l
∝

j

e

(

−

1

3

)

. Here, we extend this model to show that the optical absorption intensity should follow a

1

3

power law behavior with current density, and we perform TIRAS measurements to confirm this behavior. By altering the ionic strength (salt concentration) of our electrolyte solution to control the current density, we find that at higher concentrations a scaling of approximately

1

3

power is observed. However, the scaling is linear at lower concentrations, which we show is due to the transient response of the TIRAS experiment operating in a modulated mode. Ultimately, the experimentally-confirmed scaling law predicts approximate upper limits of penetration depth and interfacial concentration for solvated electrons, findings essential for tailoring plasma-liquid systems for specific applications.
Measurement of the third-order transport coefficient in N2 and its effect on the longitudinal diffusion coefficient measured from the arrival-time spectra of an electron swarm
Authors: Kawaguchi Satoru , Nakata Noriyuki , Satoh Kazushi , Takahashi Kazuhiro , Satoh Kohki
Published: January 2021

Arrival-time spectra (ATS) of an electron swarm in N2 from 50 Td to 700 Td (1 Td = 10−17 Vcm2) were measured by double-shutter drift tube, and then the first Townsend ionization coefficient, mean-arrival-time drift velocity, longitudinal diffusion coefficient, and longitudinal third-order transport coefficient were obtained from the measured ATS. This is the first successful measurement of the third-order transport coefficient in a gas. Furthermore, we went back to an expression of the longitudinal diffusion coefficient in terms of the α parameter, which is the electron transport coefficient derived from ATS, and then demonstrated that the third-order and higher-order electron transport coefficients, which are traditionally ignored in the electron swarm experiment, should be considered to obtain the longitudinal diffusion coefficient properly at moderate and high reduced electric fields.
Numerical simulation of vertical tunnelling field-effect transistors charge-trapping memory with TCAD tools
Authors: Cao Yang , Tian Guoliang , Sandip Majumdar , Bi Jinshun , Xi Kai , Li Bo
Published: January 2021

A novel vertical tunnelling field-effect transistor (TFET) based on silicon-oxide-nitride-oxide-silicon (SONOS) non-volatile memory device, named as VT-SONOS, is proposed and investigated using TCAD simulations. Different from traditional planar TFET-based SONOS memory, the VT-SONOS device is programmed via band-to-band tunnelling for vertical pocket and Fowler–Nordheim tunnelling for both pocket/bottom oxide (OXb) and channel/OXb regions, which leads to a steeper subthreshold swing (SS) and a larger on-state current (I
ON). The device structure is constructed using Sentaurus TCAD tools, and I
D–V
G characteristics were extracted using TCAD tools. Obtained SS value is 102.09 mV dec−1, while the I
ON was 3.02 × 10−4 A. The memory window was 2.95 V, showing more dependence on programming pulse height (V
gp) than erasing pulse height (V
ge). Furthermore, 10-year retention characteristics were studied to investigate critical reliability issue. About 60% of the initial trapped charges remained in the device after unbiased 3.15 × 108 s (10 years) storage.
Influence of oxygen flow during sputtering process on the electrical properties of Ga-doped InZnSnO thin film transistor
Authors: Yang Hui , Su Jinbao , Zhang Xiqing
Published: January 2021

This work presents the electrical properties of amorphous gallium-doped indium zinc tin oxide (Ga-IZTO) thin film transistors (TFTs), as a function of O2 flow rate (Ar/O2), during the sputtering process of the channel layer. As the O2 flow rate increased from 30:0 to 30:7, the saturation mobility (

μ

SAT) monotonically degraded from 31.5 cm2V−1s−1 to 12.0 cm2V−1s−1, the threshold voltage (V
TH) shifted from 0.8 V to 6.8 V, and the V
TH shift (ΔV
TH) induced by the negative bias stress improved from −7.0 V to −2.8 V. X-ray diffraction analysis indicated that the
microstructure of all the films is amorphous, which is independent of O2 flow rate. Transmittance spectra reflected that the average transmittance of the thin film is sensitive to the O2 flow rate and decreases as the O2 flow rate increases. XPS analysis revealed that the density of oxygen vacancies is reduced, and the oxygen lattices are enhanced as the O2 flow rate increases. The Hall effect measurements indicated that the carrier concentration (n) was reduced with increasing O2 flow rate. These results show that the electrical properties of Ga-IZTO TFTs can be easily tuned by the O2 flow rate during the sputtering process. The related mechanism for the variations of electrical properties of Ga-IZTO TFT has been discussed in detail.
A finite beam element multifunctional fabric modeling framework demonstrated with SMA knitted actuators
Authors: Eschen K , Weinberg C , Abel J
Published: January 2021

Multifunctional textiles have gained recent attention due their intrinsic properties that provide actuator, energy dampening, or sensory capabilities within small form factor textiles without external attachments. Such technologies are specifically appealing for medical and aerospace wearables, where active compression, haptic feedback, or the tracking of bodily functions are important tasks that are ideally conducted in a minimally-intrusive fashion. Current design capabilities of multifunctional textile are limited as present predictive tools lack accuracy and universality. This paper presents a finite beam element modeling tool for shape memory alloy (SMA) knitted architectures. The temperature-dependent variation of material properties within the SMA knitted loop affects the macroscopic force-extension behavior of SMA knitted architectures leading to an actuated and a relaxed knitted architecture response. This difference is exploited as the active property in SMA knitted architectures. The modeling architecture defines interfaces between sub-models organized in modules, specifically the material constitutive module, repetitive unit cell module, manufacturing module, contact module, and a boundary condition module. The SMA knitted architecture is modeled utilizing a 1D SMA constitutive model, quarter loop knit unit cell, a differential geometry-based manufacturing model, while assuming 3D Coulomb friction conditions. Kinematically-suitable boundary conditions are applied and the simulation predictions are compared quantitatively to macroscopic tensile experimental results, as well as qualitatively to microscopic x-ray diffraction phase analysis. The verification against experimental data supports the ability of the modeling tool to accurately predict the SMA knitted architecture thermo-mechanical performance with mean force-extension errors of less than 5%. The modeling tool provides the basis to understand, design, and optimize the lightweight, large force and deformation SMA knitted actuator textiles for novel applications. Additionally, the multifunctional textile modeling tool is implemented based on highly interchangeable sub-models to create synergies and propel the modeling of any multifunctional textile.
Smart polyimide with recovery stress at the level of high temperature shape memory alloys
Authors: Kong Deyan , Li Jie , Guo Anru , Yu Jianxin , Xiao Xinli
Published: January 2021

Recovery stress is important for smart shape memory materials (SMMs) and low recovery stress of shape memory polymers hinders their applications badly, while high temperature shape memory alloys (HTSMAs) are very difficult to be obtained. In order to obtain high temperature SMM with high recovery stress, convenient preparation methods, low cost and good workability, shape memory polyimide with high recovery stress (HRSMPI) at the level of HTSMA is prepared by reinforcing smart polyimide matrix with carbon fiber cloth (CFC) in common lab furnace. The HRSMPI possesses unique sandwich structure with good interfacial bonding between the matrix and filler. It exhibits high glass transition temperature of 300 °C, shape fixity of 90.6% and shape recovery of 92.2%. The recovery stress of HRSMPI is 116 MPa, close to those of some HTSMAs. The primitive actuator made of HRSMPI can overturn metal sheet 147 times heavier than itself, similar to the commercial TiNiHf HTSMA. Meanwhile, its density is 0.96 g cm−3, less than 1/6 of that of TiNiHf. The elastic strain energy is mainly stored in CFC and then released as recovery stress under constrained shape recovery, and HRSMPI has great potential in practical applications.
Magnetization loss of no-insulation coil for an electrodynamic suspension system
Authors: Wang Xueliang , Sheng Jie , Zhong Zhuoyan , Wu Wei , Li Xiao-Fen , Jin Zhijian , Hong Zhiyong
Published: January 2021

A high-temperature superconducting no-insulation (NI) coil, with its self-protection property, high engineering current density and unique demagnetization property, becomes a potential candidate for an electrodynamic suspension (EDS) system. Compared with the applications in high field magnets, the NI coil used in the EDS system is considered as working in a dynamic state, the magnetization loss generated in the NI coil is essential for the design of a cryogenic system. This paper presents the study on AC magnetization loss of NI coils by both numerical and experimental methods. Firstly, a 3D finite element numerical model representing the full geometry of the NI coil is built to analyse the effect of field frequency, field magnitude, as well as the radial characteristic resistance. Then, systematic discussions are conducted to figure out the working mechanism of NI coils. Finally, a calibration-free method testing platform is installed to validate the numerical model, and a modified model is proposed to represent the non-uniform radial characteristic resistance caused by stress distribution. The conclusions of this paper will be used in the future optimization of NI coils and the cryogenic design of the EDS system.
Strong pinning at high growth rates in rare earth barium cuprate (REBCO) superconductor films grown with liquid-assisted processing (LAP) during pulsed laser deposition
Authors: Feighan J , Lai M H , Kursumovic A , Zhang D , Wang H , Lee J H , Moon S , MacManus-Driscoll J L
Published: January 2021

We present a simple liquid-assisted processing (LAP) method, to be used in situ during pulsed laser deposition growth to give both rapid growth rates (50 Hz deposition leading to >250 nm min−1 with a single plume) and strong pinning (improved ×5–10 at 30 K and below, over plain standard YBCO films grown at similar rates). Achieving these two important features simultaneously has been a serious bottleneck to date and yet for applications, it is critical to overcome it. The new LAP method uses a non-stoichiometric target composition, giving rise to a small volume fraction of liquid phase during film growth. LAP enhances the kinetics of the film growth so that good crystalline perfection can be achieved at up to 60× faster growth rates than normal, while also enabling artificial pinning centres to be self-assembled into fine nanocolumns. In addition, LAP allows for RE mixing (80% of Y with 20% of Yb, Sm, or Yb + Sm), creating effective point-like disorder pinning centres within the rare earth barium cuprate lattice. Overall, LAP is a simple method for use in pulsed laser deposition, and it can also be adopted by other in situ physical or vapour deposition methods (i.e. MOCVD, evaporation, etc) to significantly enhance both growth rate and performance.
The quantum marginal problem for symmetric states: applications to variational optimization, nonlocality and self-testing
Authors: Aloy Albert , Fadel Matteo , Tura Jordi
Published: January 2021

In this paper, we present a method to solve the quantum marginal problem for symmetric d-level systems. The method is built upon an efficient semi-definite program that uses the compatibility conditions of an m-body reduced density with a global n-body density matrix supported on the symmetric space. We illustrate the applicability of the method in central quantum information problems with several exemplary case studies. Namely, (i) a fast variational ansatz to optimize local Hamiltonians over symmetric states, (ii) a method to optimize symmetric, few-body Bell operators over symmetric states and (iii) a set of sufficient conditions to determine which symmetric states cannot be self-tested from few-body observables. As a by-product of our findings, we also provide a generic, analytical correspondence between arbitrary superpositions of n-qubit Dicke states and translationally-invariant diagonal matrix product states of bond dimension n.
Forming-free resistive switching in ferroelectric Bi
0.97
Y
0.03
Fe
0.95
Sc
0.05
O
3 film for RRAM application
Authors: Jena A K , Mohanty Himadri Nandan , Mohanty J
Published: January 2021

Electromechanical and resistive switching properties were investigated in ferroelectric rhombohedral Bi
0.97
Y
0.03
Fe
0.95
Sc
0.05
O
3 (BYFSO) film, grown on fluorine-doped tin oxide coated glass substrate. Piezoforce microscopy images of the BYFSO film after the electrical writing indicates the ferroelectric domains were switched completely towards the upward and downward direction at ± 8 V DC bias voltage, which is analogous to the ferroelectric hysteresis curve. The resistive switching effect was investigated on the Ag/BYFSO/FTO RRAM device configuration through conventional I − V characteristics. The charge transport process in Ag/BYFSO/FTO resistive device is transformed from Ohmic to space charge limited current conduction mechanism. The endurance characteristics ensure a stable bipolar resistive switching effect with a large memory window of OFF/ON
ratio about ∼100 for 50 repeatable testing cycles. From the impedance spectroscopy analysis, it is observed that the bulk resistance plays a significant role during the SET-RESET process, by large degradation of resistance from megaohm (high resistance state) to kiloohm (low resistance state). The oxygen vacancy induced conductive filaments are responsible for achieving the various resistive states in the device.
Two-dimensional square-Au2S monolayer: A promising thermoelectric material with ultralow lattice thermal conductivity and high power factor*
Authors: Zhang Wei , Zhang Xiao-Qiang , Liu Lei , Wang Zhao-Qi , Li Zhi-Guo
Published: January 2021

The search for new two-dimensional (2D) harvesting materials that directly convert (waste) heat into electricity has received increasing attention. In this work, thermoelectric (TE) properties of monolayer square-Au2S are accurately predicted using a parameter-free ab initio Boltzmann transport formalism with fully considering the spin–orbit coupling (SOC), electron–phonon interactions (EPIs), and phonon–phonon scattering. It is found that the square-Au2S monolayer is a promising room-temperature TE material with an n-type (p-type) figure of merit ZT = 2.2 (1.5) and an unexpected high n-type ZT = 3.8 can be obtained at 600 K. The excellent TE performance of monolayer square-Au2S can be attributed to the ultralow lattice thermal conductivity originating from the strong anharmonic phonon scattering and high power factor due to the highly dispersive band edges around the Fermi level. Additionally, our analyses demonstrate that the explicit treatments of EPIs and SOC are highly important in predicting the TE properties of monolayer square-Au2S. The present findings will stimulate further the experimental fabrication of monolayer square-Au2S-based TE materials and offer an in-depth insight into the effect of SOC and EPIs on TE transport properties.
Prediction of scandium tetraboride from first-principles calculations: Crystal structures, phase stability, mechanical properties, and hardness*
Authors: Chu Bin-Hua , Zhao Yuan
Published: January 2021

Using the evolutionary methodology for crystal structure prediction, we have predicted the orthorhombic Cmcm and Pnma phases for ScB4. The earlier proposed CrB4-, FeB4-, MnB4-, and ReP4-type structures for ScB4 are excluded. It is first discovered that the Cmcm phase transforms to the Pnma phase at about 18 GPa. Moreover, both phases are dynamically and mechanically stable. The large bulk modulus, shear modulus, and Young’s modulus of the two phases make it an optimistic low compressible material. Moreover, the strong covalent bonding nature of ScB4 is confirmed by the ELF analysis. The strong covalent bonding contributes greatly to its stability.
Degradation of gate-recessed MOS-HEMTs and conventional HEMTs under DC electrical stress*
Authors: Yuan Yi-Dong , Zhao Dong-Yan , Cao Yan-Rong , Wang Yu-Bo , Shao Jin , Chen Yan-Ning , He Wen-Long , Du Jian , Wang Min , Peng Ye-Ling , Zhang Hong-Tao , Fu Zhen , Ren Chen , Liu Fang , Zhang Long-Tao , Zhao Yang , Lv Ling , Zhao Yi-Qiang , Zheng Xue-Feng , Zhou Zhi-Mei , Wan Yong , Ma Xiao-Hua
Published: January 2021

The performance degradation of gate-recessed metal–oxide–semiconductor high electron mobility transistor (MOS-HEMT) is compared with that of conventional high electron mobility transistor (HEMT) under direct current (DC) stress, and the degradation mechanism is studied. Under the channel hot electron injection stress, the degradation of gate-recessed MOS-HEMT is more serious than that of conventional HEMT devices due to the combined effect of traps in the barrier layer, and that under the gate dielectric of the device. The threshold voltage of conventional HEMT shows a reduction under the gate electron injection stress, which is caused by the barrier layer traps trapping the injected electrons and releasing them into the channel. However, because of defects under gate dielectrics which can trap the electrons injected from gate and deplete part of the channel, the threshold voltage of gate-recessed MOS-HEMT first increases and then decreases as the conventional HEMT. The saturation phenomenon of threshold voltage degradation under high field stress verifies the existence of threshold voltage reduction effect caused by gate electron injection.
Low-threshold bistable reflection assisted by oscillating wave interaction with Kerr nonlinear medium*
Authors: Zhang Yingcong , Cai Wenjuan , Wang Xianping , Yuan Wen , Yin Cheng , Li Jun , Luo Haimei , Sang Minghuang
Published: January 2021

Owing to the enormously enhanced oscillating wave, a minute variation of the incident light intensity will give rise to a change in the dielectric constant of the Kerr nonlinear medium and lead to a bistable reflection with an ultra-low threshold intensity, which is closely related to the angle of incidence and the thickness of the Kerr nonlinear medium. The criterion for the existence of optical bistability is derived. Our bistability scheme is simple and not limited to the TM-polarization.
In-medium pion dispersion relation and medium correction of

near the threshold energy of pion production *
Authors: Cui Ying , Zhang Ying-Xun , Li Zhu-Xia
Published: January 2021

Transport models cannot simultaneously explain very recent data on pion multiplicities and pion charged ratios from central collision of Sn+Sn at 0.27 A GeV. This stimulates further investigations on the pion dispersion relation, in-medium

cross sections, and

decay widths near the threshold energy or at subthreshold energy of pion production in isospin asymmetric nuclear matter. In this study, the pion dispersion relation, in-medium

cross section, and

decay width near the threshold energy are investigated in isospin asymmetric nuclear matter by using the one-boson-exchange model. With the consideration of the energy conservation effect, the in-medium

cross sections are enhanced at

GeV in a nuclear medium. The prediction of pion multiplicity and

ratios near the threshold energy could be modified if this effect is considered in transport model simulations.
Remote radio control of insect flight reveals why beetles lift their legs in flight while other insects tightly fold
Authors: Kosaka Takumi , Gan Jia Hui , Long Le Duc , Umezu Shinjiro , Sato Hirotaka
Published: January 2021

In the research and development of micro air vehicles, understanding and imitating the flight mechanism of insects presents a viable way of progressing forward. While research is being conducted on the flight mechanism of insects such as flies and dragonflies, research on beetles that can carry larger loads is limited. Here, we clarified the beetle midlegs' role in the attenuation and cessation of the wingbeat. We anatomically confirmed the connection between the midlegs and the elytra. We also further clarified which pair of legs are involved in the wingbeat attenuation mechanism, and lastly demonstrated free-flight control via remote leg muscle stimulation. Observation of multiple landings using a high-speed camera revealed that the wingbeat stopped immediately after their midlegs were lowered. Moreover, the action of lowering the midleg attenuated and often stopped the wingbeat. A miniature remote stimulation device (backpack) mountable on beetles was designed and utilized for the free-flight demonstration. Beetles in free flight were remotely induced into lowering (swing down) each leg pair via electrical stimulation, and they were found to lose significant altitude only when the midlegs were stimulated. Thus, the results of this study revealed that swinging down of the midlegs played a significant role in beetle wingbeat cessation. In the future, our findings on the wingbeat attenuation and cessation mechanism are expected to be helpful in designing bioinspired micro air vehicles.
Understanding the combined impacts of weeds and climate change on crops
Authors: Vilà Montserrat , Beaury Evelyn M , Blumenthal Dana M , Bradley Bethany A , Early Regan , Laginhas Brittany B , Trillo Alejandro , Dukes Jeffrey S , Sorte Cascade J B , Ibáñez Inés
Published: January 2021

Crops worldwide are simultaneously affected by weeds, which reduce yield, and by climate change, which can negatively or positively affect both crop and weed species. While the individual effects of environmental change and of weeds on crop yield have been assessed, the combined effects have not been broadly characterized. To explore the simultaneous impacts of weeds with changes in climate-related environmental conditions on future food production, we conducted a meta-analysis of 171 observations measuring the individual and combined effects of weeds and elevated CO2, drought or warming on 23 crop species. The combined effect of weeds and environmental change tended to be additive. On average, weeds reduced crop yield by 28%, a value that was not significantly different from the simultaneous effect of weeds and environmental change (27%), due to increased variability when acting together. The negative effect of weeds on crop yield was mitigated by elevated CO2 and warming, but added to the negative effect of drought. The impact of weeds with environmental change was also dependent on the photosynthetic pathway of the weed/crop pair and on crop identity. Native and non-native weeds had similarly negative effects on yield, with or without environmental change. Weed impact with environmental change was also independent of whether the crop was infested with a single or multiple weed species. Since weed impacts remain negative under environmental change, our results highlight the need to evaluate the efficacy of different weed management practices under climate change. Understanding that the effects of environmental change and weeds are, on average, additive brings us closer to developing useful forecasts of future crop performance.
Long term impacts of transitions in charcoal production systems in tropical biomes
Authors: van ‘t Veen Hanneke , Eppinga Maarten Boudewijn , Mwampamba Tuyeni Heita , Ferreira Dos Santos Maria João
Published: January 2021

Mitigation of greenhouse gas emissions through transitions to biomass-based renewable energy may result in higher land needs, affecting ecosystem services and livelihoods. Charcoal is a biomass-based renewable energy that provides energy for hundreds of millions of households worldwide and generates income for 40 million people. However, it currently causes up to 7% of the global deforestation rate. In the absence of affordable alternative fuels, it is necessary to identify conditions that foster sustainable charcoal production. In this study, we (a) develop a stylized model that simulates feedbacks between forest biomass and charcoal production, and (b) use the model to examine the effects of interventions that foster sustainable charcoal systems through transitions to communal management or private systems, increases in carbonization efficiency and charcoal demand reductions. Our model simulations suggest that at low demand, a transition is unnecessary. At intermediate to high demands, interventions that increase carbonization efficiency and/or reduce demand should be combined with transitions to communal management (at intermediate forest biomass levels) or private systems (at low forest biomass levels) to ensure long-term sustainability of charcoal systems and avoid collapse within 100 years. These results highlight multiple pathways for sustainable charcoal production systems tailored to meet supply and demand. All pathways are feasible across tropical biomes and could foster the simultaneous continuation of forests and charcoal production in the near future.
Spark plasma sintering of Si3N4-YAG nanocomposite
Authors: Andreev P V , Rostokina E Ye , Alekseeva L S , Murashov A A , Boldin M S , Balabanov S S
Published: January 2021

Spark plasma sintering (SPS) of mixtures based on silicon nitride nanopowders (Si3N4) was considered. A method for creating a mixture based on nanosized Si3N4 and a sintering additive of yttrium-aluminum garnet (YAG, Al5Y3O12) was developed. The precursor of the sintering additive was formed by the method of spray drying using a mixture of colloidal solutions of Al5(NO3)3(OH)12 and Y(OH)2(CH3COO). The produced mixture samples were studied by X-ray diffraction analysis and SEM. The kinetics of the SPS of the prepared mixtures was studied. The effect of preliminary annealing (up to 1000 °C) of the mixture on the formation of the YAG sintering additive have been considered, as well as the method of reactive synthesis of the sintering additive in the SPS process. It was found out that sintering of the annealed mixture does not allow forming high density ceramics. As a result of reactive sintering, ceramics based on Si2N2O were formed.
Laser fusion of aluminum-alumina composites obtained in the vortex layer apparatus
Authors: Nalivaiko A , Ozherelkov D , Morozova A , Shinkaryov A , Gromov A
Published: January 2021

The current study is devoted to laser fusion of aluminum-matrix composites with 3 wt. % of alumina obtained in the vortex layer apparatus. The mixing parameters and the distribution of alumina in the composite structure were studied. Three parameters of laser fusion for plate synthesis were used. The finest results were achieved using a volumetric energy density of 24 J/mm3 with 370 W laser power. The maximum mechanical properties of the samples synthesized by the optimal parameters were: UTS = 384 ± 5 MPa; Ef = 0.54 ± 0.1 %.
On the formation of AlSiMgCu/quasicrystal powder composite single tracks by selective laser melting
Authors: Ozherelkov D Yu , Nalivaiko A Yu , Gromov A A , Solodov D O , Komissarov A A , Shinkaryov A S , Morozova A I
Published: January 2021

The process of selective laser melting (SLM) of an Al-Si-Mg-Cu powder composite with the addition of quasicrystal reinforcements under conditions of a limited powder amount was investigated. The morphology and microhardness of the obtained scan single tracks were discussed, and the optimal sintering parameters were found to be in the Linear Energy Density (LED) range 0.21-0.30 J/mm. The following SLM parameters: P = 370 W and v = 1650 mm/s given the optimal characteristics of scan single tracks geometry with less defects. The obtained composites exhibited an improved hardness with the highest values of 235 HV with the 8% of reinforcements in the powder mixture.
Structure formation of titanium alloys during vacuum-arc surfacing
Authors: Permyakov G L , Olshanskaya T V , Krivonosova E A , Trushnikov D N
Published: January 2021

The work is based on wire vacuum-arc surfacing as one of the technologies for additive manufacturing. The results of the formation of structure and properties of a high-temperature titanium alloy of the Ti-Al-V-Mo-Zr system during vacuum-arc surfacing are presented. The structure of the surfaced materials consists of dendritic grains that are oriented in the direction opposite to heat removal. Some banding of the structure is observed. There is no porosity in the deposited layers for all surfacing modes. It was determined that a decrease in the surfacing current promotes an increase in the dispersion of the α-phase plates, which is accompanied by an increase in microhardness. With such a thermal cycle of surfacing, conditions are created for the formation of a favorable fine-dispersed martensitic structure with narrow α-colonies of small needles of the α-phase, providing a high microhardness at the level of 400HV.
Study of phase formation and properties of high-entropy carbide HfTaTiNbZrC5 obtained by selfpropagating high-temperature synthesis
Authors: Sedegov A S , Bobojanov A R , Vorotilo S , Kuskov K V , Moscovskikh D O
Published: January 2021

This work is devoted to the study of the combustion synthesis mechanism in complex multi-component systems using the quenching of the combustion front in a copper block. Bulk specimens were produced by reactive spark plasma sintering (R-SPS) of mechanically activated mixtures as well as by SPS of high-entropy ceramics obtained by combustion synthesis. The resistance of high-entropy carbides towards oxidation was studied in relation to the number of metallic constituents.
Effect of carbon content, deformation and annealing on the structure and properties of interstitial TRIP high-entropy alloys
Authors: Shaysultanov D G , Raimov K Sh , Stepanov N D
Published: January 2021

In this work, the effect of carbon content on the structure and mechanical properties of Fe(50-x)Mn30Co10Cr10Cx (x=0; 0.5; 1.0 at.%) interstitial high entropy alloys was studied. In the as-cast condition, the alloys were composed of the face centred cubic (fcc) and hexagonal close packed (hcp) phases; the amount of the hcp phase decreased from 46% to 20% as the carbon concentration increased from 0 to 1 at.%. The carbon content had a limited effect on the strength of the alloys, yet the ductility was enhanced significantly as the result of interstitial alloying. Furthermore, Fe49Mn30Co10Cr10C1 alloy was cold rolled to a reduction of 56% reduction and annealed at 700-900°C for 1 hour. After cold working, the alloy has attained almost fully the hcp structure. Annealing resulted in (i) transformation of the deformation-induced hcp phase into fcc; (ii) development of recovery and recrystallization; (iii) precipitation of Cr-rich M23C6 carbides. The cold-rolled alloy was very strong but brittle; annealing resulted in softening and increase of the ductility. The relationships between the chemical composition, structure and mechanical properties of the alloys are briefly discussed.
Synthesis of the high-entropy (BiSbSe1.5Te1.5)1-x
Cu
x
compound promising for thermoelectric applications
Authors: Vasil’ev A E , Yaprintsev M N , Ivanov O N , Zhezhu M V , Yapryntseva E N
Published: January 2021

Single phase and nanosized powders of high-entropy (BiSbSe1.5Te1.5)1-x
Cu
x
compound with x=0; 0.3, 0.6 were synthesized by using soft chemistry approaches. Owing to its low thermal conductivity, this compound is promising for thermoelectric applications. The synthesized powders were used to prepare bulk samples totally suitable for testing thermoelectric properties.
Structure and mechanical properties of near-eutectic refractory Al-Cr-Nb-Ti-Zr high entropy alloys
Authors: Yurchenko N , Panina E , Salishchev G , Stepanov N
Published: January 2021

In this study, the structure and mechanical properties of the near-eutectic refractory Al24Cr11Nb11Ti37Zr17, Al20Cr20Nb25Ti25Zr10, and Al28Cr15Nb15Ti20Zr22 (at.%) high entropy alloys were investigated. Both the Al24Cr11Nb11Ti37Zr17 and Al20Cr20Nb25Ti25Zr10 alloys had a hypoeutectic structure, while the Al28Cr15Nb15Ti20Zr22 alloy had a hypereutectic one. The proeutectic phase in the Al24Cr11Nb11Ti37Zr17 and Al20Cr20Nb25Ti25Zr10 alloys was the ordered B2 phase and in the Al28Cr15Nb15Ti20Zr22 alloy – the C14 Laves phase. In all three alloys, the eutectic regions possessed a fine lamellar structure composed of a mixture of the C14 Laves and B2 phases. The densities of the alloys were 5.20-5.89 g/cm3. The Al24Cr11Nb11Ti37Zr17 and Al28Cr15Nb15Ti20Zr22 alloys were extremely brittle at 22°C, while the Al20Cr20Nb25Ti25Zr10 alloy showed some ductility (ε = 0.7%) and high yield strength of 1830 MPa. At 800°C, all alloys became ductile. The highest yield strength (1010 MPa) was demonstrated by the Al20Cr20Nb25Ti25Zr10 alloy and the lowest one (235 MPa) – by the Al24Cr11Nb11Ti37Zr17 alloy. The comparison between the experimental as-solidified structures and the CALPHAD predictions was made.
Nanoscale structural evolution of Al2Cu precipitates in friction-stir welded Al–Cu–Mg alloy
Authors: Zuiko I , Malopheyev S , Mironov S , Kaibyshev R
Published: January 2021

The work is devoted to FSW of cold rolled AA2519. The non-uniform distribution of all second phase precipitates (including coherent θ″ and non-coherent θ) was shown via the TEM-technique. The nucleation of the stable θ-phase, along with decreased dislocation density, led to a drop (∼60 HV0.2) in the microhardness of the nugget zone.
Robotized assembly and inspection of composite fuselage panels: the LABOR project approach
Authors: Caterino Mario , Chiacchio Pasquale , Cristalli Cristina , Fera Marcello , Lettera Gaetano , Natale Ciro , Nisi Matteo
Published: January 2021

The aerospace manufacturing is looking at ways to change their production processes in order to improve costs, flexibility and efficiency. The LABOR project, acronym for Lean robotized AssemBly and cOntrol of composite aeRostructures, aims at introducing robotic solutions for the assembly line of fuselage panels adopting medium size robots equipped with smart tools, Human Robot collaboration approach and a distributed software architecture. The system consists of a jig that holds the panel to be assembled, two 6-axis robots mounted on moving platforms in order to reach the whole panel and real time measurements to perform the quality control of the assembled components. The cell automatically performs the referencing of the robot working area on the basis of the recognition of geometric features of the parts to be coupled (edges, holes, etc.) through the use of 3D smart inspection tools. After the ”one shot” drilling and countersinking operations, the hole is processed to guarantee a high standard of the process. Installation and sealing of the fastener complete the working cycle. Furthermore, an advanced multimodal perception system monitors the collaborative workspace in real time for safe human-robot collaboration (HRC) tasks. The project started in March 2018 as part of the European Clean Sky 2 research program. Three partners – LOCCIONI, UNICAMPANIA and UNISA – are developing the prototype cell in collaboration with LEONARDO S.P.A. that is the Topic Manager.
Development and trend of unified mechanism-based materials modelling for creep age forming of aluminium alloys
Authors: Wang Xi , Li Yong , Chen Baoguo , Shi Zhusheng
Published: January 2021

Materials modelling plays an important role for sprinback compensation and tool surface design in creep age forming (CAF). This review aims to provide perspective on the development and trend of materials modelling for CAF of aluminium alloys. Recently proposed unified constitutive equations for creep-ageing behaviour of aluminium alloys during CAF by integrating microstructural evolution and hardening effects are reviewed. The modelling methods and developing trend to quantitively reflect the relationship between the microstructural evolutions and macro creep-ageing behaviour of materials during CAF are discussed.
Integration and evaluation of a meander-shaped fibre-optical sensor in GFRP coupons
Authors: Preisler A , Wolf-Monheim F , Kaiser D , Wojtczyk R , Dafnis A , Schröder K-U , David W , Zandbergen P
Published: January 2021

Fibre-reinforced plastics are attracting more and more attention also in non-aviation sectors. The possible formation of internal damage and its difficult detection thus simultaneously increases the need for structural health monitoring. In this case especially fibre-optical sensors possess an enormous potential. In the previous work the use of a meander-shaped sensor layout was proposed, utilizing strain in longitudinal direction for loads monitoring and distinct measuring sections in zero-strain direction for structural health monitoring. In the present work, the proposed meander-shaped sensor layout is integrated inside unidirectional coupons using tailored fibre placement. Further samples without a sensor and samples with a straight sensor-fibre were also manufactured as a reference. The influence of the sensor on the static strength and stiffness is then examined in a test campaign using a three-point bending setup. In addition, the functionality of the meander-shaped sensor layout is validated.
Investigation on low velocity impact damage identification with ultrasonic techniques under different sensor network conditions
Authors: Beligni A , Cadini F , Sbarufatti C , Giglio M , Cimminiello N , Salvato P , Monaco E , Romano F
Published: January 2021

Direct or indirect damages due to foreign object impacts on aeronautical structures, represent a major concern. The problem potentially intensifies with the adoption of composite materials, especially due to Barely Visible Impact Damage (BVID). In this context, understanding whether an impact event gives rise to delamination or debonding is highly desirable in view of the optimization of the maintenance strategies and, at the same time, of the safety margins associated to the operation of the structures. One possible method to achieve this goal is that of integrating damage monitoring systems within the vehicle architecture itself. By doing so, in fact, the enhanced structural health state awareness allows the implementation of Predictive Maintenance philosophies and the possibility to detect damage with size/severity and indentation smaller than the BVID currently applied by design and certification. In this work, a simple and a stiffened carbon fiber panel are subjected to Low Velocity Impacts using falling masses to generate a structural damage. A sensor network made of Piezoelectric elements (PZT) allows the application of Ultrasonic techniques, to monitor the damaged structure and calculate signal related features called Damage Indexes (DIs). The DI capability to identify the damage is then thoroughly investigated, with specific reference to: (i) effect of signal averaging, (ii) effect of reduced sensor network configurations and (iii) effect of sensor faults.
Eddy Current and Quantum Well Effect Eddy Current Field Measurement of Carbon Fibre Raw Materials and cured parts in the Aerospace Industry
Authors: Silva C , James V , Smith C , Hansen J , Missous M , Sexton J , Watson J , Dobson J
Published: January 2021

The composite industry requires a fast and couplant free NDT methodology. The C-Flux project spearheaded by M Wright & Sons Ltd (MWS) and TWI Wales, is tackling these requirements with the development of Eddy Current NDT system developed by ETher NDE and quantum well effect eddy current field measurement (QW-ECFM) NDT system developed by AHS. FAR UK and MWS are supplying to the project standard and flawed carbon fibre composite parts up 20mm thick to refine these electromagnetic techniques. TWI is developing automated apparatuses to deploy these NDT systems for the aerospace industry.
Mesh-diverging inviscid adjoint solutions
Authors: Lozano Carlos , Ponsin Jorge
Published: January 2021

This paper describes a surprising problem encountered in the numerical solution of the Adjoint Euler equations. The basic result presented here is that certain two and three dimensional numerical solutions to the adjoint Euler equations have a value at and near the surface of wings and airfoils that depends strongly on the mesh density and which does not converge as the mesh is refined. The purpose of this paper is to characterize this problem and offer insights as to the possible explanation of this unusual behavior.