bluuebunny/crossref_metadata_2025 huggingface dataset:
High solubility of Al and enhanced thermoelectric performance due to resonant states in Fe2VAlx
Authors: Parzer M. , Garmroudi F. , Riss A. , Khmelevskyi S. , Mori T. , Bauer E.
Published: February 2022

Recently, n-type Fe2VAl-based full-Heusler systems, exhibiting high thermoelectric power factors, have sparked new interest in this material class for thermoelectric applications. In this paper, the aluminum-rich region of the L21 phasespace in Fe–V–Al is explored by a step-by-step increase in the Al content in Fe2VAlx. We reveal a promising route to improve the thermoelectric properties of p-type Heusler alloys. First, we find an ultrahigh solubility of Al in Fe2VAlx and confirm the presence of a single Heusler phase up to x = 2 using x-ray diffraction analysis and scanning electron microscopy. Second, thermoelectric transport properties, measured in a wide temperature range from 4 to 800 K, show a substantial increase in the thermopower by over 100% and a significant decrease in the thermal conductivity by up to 80% for the Al-rich samples. Detailed analysis of the carrier-concentration-dependent thermopower as well as Hall measurements indicate the formation of a resonant state at the valence band edge as a likely origin for this enhancement. This is further corroborated by density-functional-theory calculations of the electronic density of states. Our work sets the stage for p-type full-Heusler materials with enhanced thermoelectric performance, applying the principle of resonant states to this material class.
Non-equilibrium epitaxy of metastable polymorphs of ultrawide-bandgap gallium oxide
Authors: Zhang Wenrui , Zhang Jianguo , Chen Li , Wang Wei , Zhang Tan , Liu Ningtao , Xu Tao , Yang Hongxin , Ye Jichun
Published: February 2022

Precision synthesis of ultrawide-bandgap semiconductors with a desired crystal phase is of broad interest for developing advanced electronic devices. However, it is highly challenging for gallium oxide (Ga2O3), which is known for versatile crystal phase transition. Here, we report a non-equilibrium epitaxy strategy to confine the crystallization pathways of Ga2O3 toward two distinct metastable polymorphs during the pulsed laser deposition (PLD) growth. This is achieved by synergic control of the substrate orientation and intentional tin (Sn) doping, which dramatically modifies the nucleation and growth kinetics of Ga2O3. Using a-plane sapphires and a medium Sn doping level, we overcome the commonly observed growth limitations of α-phase Ga2O3 (α-Ga2O3) films that are only stable for the initial few monolayers in previous PLD studies. Instead, we stabilize epitaxial α-Ga2O3 films with excellent phase uniformity and crystallinity for a thickness beyond 200 nm. This contrasts to the otherwise formed ε-phase Ga2O3 films by simply switching the sapphire substrate orientation to c-plane regardless of the Sn doping level. Density functional theory calculations reveal the critical role of the surface energy minimization for selective stabilization of metastable phases. This study provides a perspective to improve the non-equilibrium synthesis capability for exploring emerging ultrawide-bandgap semiconductors.
How surface roughness promotes or suppresses drop splash
Authors: Zhang Haixiang , Zhang Xiwen , Yi Xian , Du Yanxia , He Feng , Niu Fenglei , Hao Pengfei
Published: February 2022

This work presents an experimental study on the splashing behaviors of drops impinging on rough solid surfaces. Most prior studies have shown the increase in surface roughness can promote the occurrence of a drop splash. Interestingly, we found two opposite effects of surface roughness on the drop splash that the increase in surface roughness can promote splash of low-viscosity drops but suppress splash of high-viscosity drops. According to the wetting state of the spreading lamella on rough surfaces, the splash regime can be classified into two modes: corona splash and prompt splash. It is found that the increase in surface roughness can promote the prompt splash but suppress the corona splash. The increase in surface roughness could provide wide channels for air to escape and suppress the corona splash. Meanwhile, the larger surface roughness could also disrupt the expanding lamella and promote the prompt splash. The dimensionless parameter Ohr can be used to distinguish two splash regimes, and the critical value Ohrc is obtained from experimental results, at which the splash regime changes from the prompt to corona splash. Emphatically, we obtain the splash criteria in two regions, which could reflect the opposite effects of surface roughness on the drop splash and successfully characterize the splashing behaviors in this work and previous studies. The results of this work are expected to provide valuable insights to control the drop splash in industrial applications.
Structural, electronic, and transport properties of 1D Ta2Ni3Se8 semiconducting material
Authors: Chung You Kyoung , Jeon Jiho , Lee Junho , Choi Jae-Young , Huh Joonsuk
Published: February 2022

Due to their unique properties and potential applications, van der Waals (vdW) crystals with covalently bonded building blocks through vdW interactions have sparked widespread interest. In this article, we introduce a Ta2Ni3Se8 material as an example of an emerging one-dimensional (1D)-vdW-based material. Recently, it was demonstrated that bulk Ta2Ni3Se8 crystals may be effectively exfoliated into a few-chain-scale nanowires using simple mechanical and liquid-phase exfoliation. We performed density-functional theory calculations to get a better understanding of its electrical, magnetic, and transport properties. Theoretically, we expect that this Ta2Ni3Se8 is a semiconducting material, displaying the indirect-to-direct bandgap transition from bulk to single, as well as the band splitting and bandgap opening with the inclusion of Coulomb interaction. Based on deformation potential theory, the carrier mobility of bulk Ta2Ni3Se8 along the axis direction (a-axis) is as high as 264.00 cm2 V−1 s−1 for electrons and 119.62 cm2 V−1 s−1 for holes. The calculated carrier mobility of Ta2Ni3Se8, a 1D single nanowire, is 59.60 cm2 V−1 s−1 for electrons and 42.90 cm2 V−1 s−1 for holes, which is comparable to that of other 1D materials. This confirms that a recently developed field-effect transistor based on Ta2Ni3Se8 nanowires exhibits maximum experimental mobilities of 20.3 and 3.52 cm2 V−1 s−1 for electrons and holes, respectively. On the basis of the obtained intriguing properties of 1D vdW Ta2Ni3Se8 material, it is expected to be a potential candidate for additional 1D materials as channel materials.
High-electric-field behavior of the metal-insulator transition in TiS3 nanowire transistors
Authors: Randle M. D. , Lipatov A. , Datta A. , Kumar A. , Mansaray I. , Sinitskii A. , Singisetti U. , Han J. E. , Bird J. P.
Published: February 2022

We investigate the behavior of the metal-insulator transition (MIT) in TiS3 nanowire field-effect transistors, in the strongly nonequilibrium limit that has, thus far, largely been neglected. Under high electric fields within the TiS3 channel (≤115 kV/cm), we observe the emergence of a critical fixed point, separating insulating and metallic regions in the transfer curves of the device. The critical gate voltage that defines this fixed point evolves systematically with the drain bias (field), allowing us to map out a phase diagram that identifies the conditions for metallicity or for insulating behavior. Dependent upon the choice of the gate voltage used to tune the carrier concentration in the nanowire, the existence of the field-induced MIT allows the TiS3 to be either insulating or metallic over an extensive range of temperature. The possible connection of this strongly nonequilibrium state to some form of charge density wave is discussed.
Negative thermal expansion of two-dimensional magnets
Authors: Liu Shuang , Long Meng-Qiu , Wang Yun-Peng
Published: February 2022

Thermal expansion phenomena are of both engineering and fundamental interest. The conventional theory of thermal expansion of solids considers anharmonic phonon effects but largely neglects other kind of elementary excitations. A recent experiment reported a negative thermal expansion (NTE) of a two-dimensional magnet CrBr3 at low-temperatures. Our first-principles calculations, if only the effects of atomic vibrations are considered, predict a low-temperature NTE but lower by several orders of magnitude than experimental data. We propose magnetic excitations (magnons) as another important contributor to the NTE. We extend the theory of thermal expansion by including the contribution from magnons to Helmholtz free energy. First-principles calculations based on this theory confirm the dominate role of magnons in the negative thermal expansion of CrBr3 as well as in other two-dimensional magnets.
Land-use trajectories for sustainable land system transformations: Identifying leverage points in a global biodiversity hotspot
Authors: Martin Dominic Andreas , Andrianisaina Fanilo , Fulgence Thio Rosin , Osen Kristina , Rakotomalala Anjaharinony Andry Ny Aina , Raveloaritiana Estelle , Soazafy Marie Rolande , Wurz Annemarie , Andriafanomezantsoa Rouvah , Andriamaniraka Harilala , Andrianarimisa Aristide , Barkmann Jan , Dröge Saskia , Grass Ingo , Guerrero-Ramirez Nathaly , Hänke Hendrik , Hölscher Dirk , Rakouth Bakolimalala , Ranarijaona Hery Lisy Tiana , Randriamanantena Romual , Ratsoavina Fanomezana Mihaja , Ravaomanarivo Lala Harivelo Raveloson , Schwab Dominik , Tscharntke Teja , Zemp Delphine Clara , Kreft Holger
Published: February 2022

Significance

Finding entry points where policy has strong leverage to transform land systems for people and nature is pivotal. We develop an innovative framework to identify and evaluate such leverage points along land-use trajectories that account for path dependency. Applied to the biodiversity hotspot Madagascar, the framework reveals three leverage points: Two leverage points are associated with trade-offs between biodiversity, ecosystem services, and agricultural productivity, while the third entails cobenefits. Swift policy action is required, as path dependency caused by forest loss may soon put two leverage points out of reach. We argue that such closing windows of opportunity may be common, but often overlooked, calling for a wider consideration of path dependency in land-system science.
A diffusion MRI-based spatiotemporal continuum of the embryonic mouse brain for probing gene–neuroanatomy connections
Authors: Wu Dan , Richards Linda J. , Zhao Zhiyong , Cao Zuozhen , Luo Wanrong , Shao Wei , Shi Song-Hai , Miller Michael I. , Mori Susumu , Blackshaw Seth , Zhang Jiangyang
Published: February 2022

Significance

We established an ultra high-resolution diffusion MRI atlas of the embryonic mouse brains from E10.5 to E15.5, which characterizes the continuous changes of brain morphology and microstructures at mesoscopic scale. By integrating gene-expression data into the spatiotemporal continuum, we can navigate the evolving landscape of gene expression and neuroanatomy across both spatial and temporal dimensions to visualize their interactions in normal and abnormal embryonic brain development. We also identified regional clusters with distinct developmental trajectories and identified gene-expression profiles that matched to these regional domains. The diffusion MRI–based continuum of the embryonic brain and the computational techniques presented in this study offer a valuable tool for systematic study of the genetic control of brain development.
More comprehensive sex education reduced teen births: Quasi-experimental evidence
Authors: Mark Nicholas D. E. , Wu Lawrence L.
Published: February 2022

Significance

Sex education for youth in the United States has been the topic of considerable debate among researchers, policy makers, and the public at large. In this study, we focus attention on federal funding for more comprehensive sex education that was received by a mix of public and private organizations in 55 US counties. Our analyses provide population-level causal evidence that funding for more comprehensive sex education led to an overall reduction in the teen birth rate at the county level of more than 3%. This study thus contributes causal evidence relevant to ongoing debates on the potential role more comprehensive sex education may play in reducing teen births in the United States.
Sharp, localized phase transitions in single neuronal cells
Authors: Fedosejevs Carina S. , Schneider Matthias F.
Published: February 2022

Significance

Phase transitions in materials are accompanied by drastic changes in their properties. Systems abruptly become softer, more conductive, have better heat storage, or support chemical reactions more efficiently. Since changes take place over small variations in external conditions (tension, temperature, pH, calcium), they appear like an on/off switch. Here, we provide experimental evidence that membrane patches of single living cells can go through a reversible phase transition. It is extremely “sharp” (highly nonlinear), and from a thermodynamic point of view we conclude it cannot only be triggered by temperature but also by pH changes (as produced by enzymes). The results strongly support the idea that phase transitions may be a tool for living systems to control their functions even specifically.
Enhanced localized dipole of Pt-Au single-site catalyst for solar water splitting
Authors: Liu Xingyu , Hao Zhifei , Wang Haitao , Wang Tuo , Shen Zhurui , Zhang Hao , Zhan Sihui , Gong Jinlong
Published: February 2022

Significance

Single-atom or single-site catalysts have received considerable research interest in photocatalysis and many other heterogeneous catalytic processes. However, the single metal sites did not obviously change the charge transportation process of the photocatalyst and thus hardly contributed to the enhancement of charge separation and transfer. Inspired by the synergy between metal species in classical catalytic reactions, this research presents a strategy of constructing a Pt-Au binary single-site catalyst. Pt-Au binary single sites not only functioned as the catalytic reactive sites but also modulated the charge distribution and enhanced the internal electric field. The concept and the strategy of this work are expected to provide a novel perspective for improving photocatalytic charge transportation dynamics.
Intergenerational changes in Gurindji Kriol
Authors: Sloan Bodean , Meakins Felicity , Algy Cassandra
Published: February 2022

This paper explores intergenerational changes in Gurindji Kriol, in order to determine whether differences between adults and children are the result of an abrupt generational shift or an extended acquisition process. We analyse the production of Gurindji in the speech of five age groups of Gurindji Kriol speakers, using a set of 176 picture-prompt narratives from 70 different speakers. The data is analysed both synchronically (in apparent-time) and diachronically (in real-time). The synchronic snapshot of the data reveals that adults use significantly more Gurindji than children which can be interpreted as a generational shift towards Kriol. Nonetheless the real-time data shows that most children increase their use of Gurindji as they age which suggests an extended acquisition of Gurindji. Although contradictory on the surface, this study argues that these processes are occurring in tandem, with the extended acquisition of Gurindji by children slowing down the intergenerational shift towards Kriol.
Effect of unipolar pulsed electric current treatment of the melt of Al – 8 wt-% Si – 0.7 wt-% Fe alloy on iron-containing phases formation and mechanical properties of castings
Authors: Prigunova A. G. , Koshelev M. V. , Borisov A. G.
Published: February 2022

The effect of processing an Al – 8 wt-% Si – 0.7 wt-% Fe melt by a unipolar pulsed electric current on the mechanical properties of castings obtained from it has been investigated. It has been established that the complex of properties has a maximum at j = 7 A cm−2, ν = 700 Hz. The study of the microstructure of castings obtained from the melt processed in this way, compared with the structure of castings from an untreated melt, showed that treatment with current leads to a partial replacement of large β-phase into the α-phase, and reduction in the size of the remaining β-phase. It is assumed that this effect is associated with a change in the structure of the melt, increasing supercooling.
Exercise‐induced changes on exerkines that might influence brown adipose tissue metabolism in young sedentary adults
Authors: Mendez‐Gutierrez Andrea , Aguilera Concepción M. , Osuna‐Prieto Francisco J. , Martinez‐Tellez Borja , Rico Prados Ma Cruz , Acosta Francisco M. , Llamas‐Elvira Jose M. , Ruiz Jonatan R. , Sanchez‐Delgado Guillermo
Published: February 2022

In rodents, exercise alters the plasma concentration of exerkines that regulate white adipose tissue (WAT) browning or brown adipose tissue (BAT) metabolism. This study aims to analyse the acute and chronic effect of exercise on the circulating concentrations of 16 of these exerkines in humans. Ten young sedentary adults (6 female) performed a maximum walking effort test and a resistance exercise session. The plasma concentration of 16 exerkines was assessed before, and 3, 30, 60, and 120 min after exercise. Those exerkines modified by exercise were additionally measured in another 28 subjects (22 women). We also measured the plasma concentrations of the exerkines before and after a 24‐week exercise programme (endurance + resistance; 3‐groups: control, moderate‐intensity and vigorous‐intensity) in 110 subjects (75 women). Endurance exercise acutely increased the plasma concentration of lactate, norepinephrine, brain‐derived neurotrophic factor, interleukin 6, and follistatin‐like protein 1 (3 min after exercise), and musclin and fibroblast growth factor 21 (30 and 60 min after exercise), decreasing the plasma concentration of leptin (30 min after exercise). Adiponectin, atrial natriuretic peptide (ANP), β‐aminoisobutyric acid, meteorin‐like, follistatin, pro‐ANP, irisin and myostatin were not modified or not detectable. The resistance exercise session increased the plasma concentration of lactate 3 min after exercise. Chronic exercise did not alter the plasma concentration of these exerkines. In sedentary young adults, acute endurance exercise releases to the bloodstream exerkines that regulate BAT metabolism and WAT browning. In contrast, neither a low‐volume resistance exercise session nor a 24‐week training programme modified plasma levels of these molecules.

Highlights

Acute endurance exercise increases the plasma concentration of lactate, norepinephrine, brain‐derived neurotrophic factor, interleukin 6, follistatin‐like protein 1, musclin, and fibroblast growth factor 21, and decrease the plasma concentration of leptin.

The exercise‐induced change in lactate plasma concentration is positively associated with brown adipose tissue volume, glucose uptake and radiodensity.

Neither acute resistance exercise nor chronic exercise significantly alter the plasma concentration of these exerkines.

Trial registration:ClinicalTrials.gov identifier: NCT02365129.
Fluorination Increases Hydrophobicity at the Macroscopic Level but not at the Microscopic Level
Authors: Di Weishuai , Wang Xin , Zhou Yanyan , Mei Yuehai , Wang Wei , Cao Yi
Published: February 2022

Hydrophobic interactions have been studied before in detail based on hydrophobic polymers, such as polystyrene (PS). Because fluorinated materials have relatively low surface energy, they often show both oleophobicity and hydrophobicity at the macroscopic level. However, it remains unknown how fluorination of hydrophobic polymer influences hydrophobicity at the microscopic level. We synthesized PS and fluorine-substituted PS (FPS) by employing the reversible addition-fragmentation chain transfer polymerization method. Contact angle measurements confirmed that FPS is more hydrophobic than PS at the macroscopic level due to the introduction of fluorine. However, single molecule force spectroscopy experiments showed that the forces required to unfold the PS and FPS nanoparticles in water are indistinguishable, indicating that the strength of the hydrophobic effect that drives the self-assembly of PS and FPS nanoparticles is the same at the microscopic level. The divergence of hydrophobic effect at the macroscopic and microscopic level may hint different underlying mechanisms: the hydrophobicity is dominated by the solvent hydration at the microscopic level and the surface-associated interaction at the macroscopic level.
Dimension-programmable CsPbBr3 nanowires for plasmonic lasing with PDMS templated technique
Authors: Chu Kaiwen , Ma Fangyuan , Zhu Xiaojun , Jia Xiaohao , Huang Zhitao , Dong Keqian , Sun Jiaqian , Liu Kong , Jin Peng , Wang Zhijie , Qu Shengchun
Published: February 2022

Lead halide perovskites have superior gain properties, and they can be mass produced into nanowire structures through chemical synthesis. The application of perovskite materials into plasmonic nanowire lasers lowers the lasing threshold and simplifies the fabrication process. However, in nearly all previous reported cases, perovskite nanowires were randomly distributed onto metallic substrate when using the method of dry-transferring or direct chemical vapor deposition. As a result, the dimensions of perovskite nanowires are random and undesired photonic mode lasing may take place instead. Here we present a method for preparing polydimethylsiloxane templated CsPbBr3 nanowires upon Au substrate in controllable dimensions with height below cutoff size, therefore advantageous for plasmonic nanowire laser applications. Additionally, low threshold plasmonic lasing is observed in ridge structure CsPbBr3 nanowire waveguide with a total height of merely 160 nm on Au substrate. A faster radiative decay rate than its photonic counterpart is evident, as well as a dominant polarization parallel to the nanowire axial solidify plasmonic lasing. This work paves the way for mass production of perovskite plasmonic nanolasers.
Electronic cloaking of confined states in phosphorene junctions
Authors: Molina-Valdovinos S , Lamas-Martínez K J , Briones-Torres J A , Rodríguez-Vargas I
Published: February 2022

We study the electronic transport of armchair (AC) and zigzag (ZZ) gated phosphorene junctions. We find confined states for both direction-dependent phosphorene junctions. In the case of AC junctions confined states are reflected in the transmission properties as Fabry–Pérot resonances at normal and oblique incidence. In the case of ZZ junctions confined states are invisible at normal incidence, resulting in a null transmission. At oblique incidence Fabry–Pérot resonances are presented in the transmission as in the case of AC junctions. This invisibility or electronic cloaking is related to the highly direction-dependent pseudospin texture of the charge carriers in phosphorene. Electronic cloaking is also manifested as a series of singular peaks in the conductance and as inverted peaks in the Seebeck coefficient. The characteristics of electronic cloaking are also susceptible to the modulation of the phosphorene bandgap and an external magnetic field. So, electronic cloaking in phosphorene junctions in principle could be tested through transport, thermoelectric or magnetotransport measurements.
Emergent force and work fluctuations in a bilayer superfluid Bose–Fermi mixture in mixed dimensions
Authors: Günay Mehmet
Published: February 2022

We investigate a system of two-atomic species in mixed dimensions, in which one species is spread in a three-dimensional space and the other species is confined in two parallel layers. The presence of atoms in three-dimensions creates an induced potential for the ones confined in layers. Depending on the scattering (coherence) length and the layer separation, the formation of p-wave pairing within the same layer or s-wave pairing between different layers has been suggested. It was shown that these pairs cannot coexist when time-reversal symmetry is on, and there appears a transition from p-wave to s-wave as the ratio of the layer separation and the effective scattering length decreases. Here, we study the thermodynamical signatures of such transition and find that with the formation of the inter-layer pairing, an emergent force to be present at the critical point and show that it can be derived from the ground state energy. This result offers a tool for experimentally realizing such transitions, and can find notable potential in the field of quantum-thermodynamics.
Surface disinfection with silver loaded pencil graphite prepared with green UV photoreduction technique
Authors: Goh Simon Chun Kiat , Wu Wenshuai , Siah Chun Fei , Phee Derek Keng Yang , Liu Aiqun , Tay Beng Kang
Published: February 2022

Carbon-based materials have been studied for their antimicrobial properties. Previously, most antimicrobial studies are investigated with suspended nanoparticles in a liquid medium. Most works are often carried out with highly ordered pyrolytic graphite. These materials are expensive and are not viable for mass use on high-touch surfaces. Additionally, highly antimicrobial silver nanoparticles are often incorporated onto substrates by chemical reduction. At times, harmful chemicals are used. In this work, low-cost graphite pencils are mechanically exfoliated and transferred onto Si substrates. The sparsely-covered graphite flakes are treated by either plasma O2 or UV irradiation. Subsequently, Ag is photo reduced in the presence of UV onto selected graphite flake samples. It is found that graphite flake surface topography and defects are dependent on the treatment process. High surface roughness and (defects density, I
D/I
G) are induced by plasma O2 follows by UV and pristine graphite flake as follows: 6.45 nm (0.62), 4.96 nm (0.5), 3.79 nm (0.47). Antimicrobial tests with E. coli reveal high killing efficiency by photoreduced Ag-on-graphite flake. The reversible effect of Ag leaching can be compensated by repeating the photoreduction process. This work proposes that UV treatment is a promising technique over that of plasma O2 in view that the latter treated surface could repel bacteria resulting in lower bacteria-killing efficiency.
Unusual pseudocapacitive lithium-ion storage on defective Co3O4 nanosheets
Authors: Avvaru Venkata Sai , Vincent Mewin , Fernandez Ivan Jimenez , Hinder Steven J , Etacheri Vinodkumar
Published: February 2022

Secondary lithium-ion batteries are restricted in large-scale applications including power grids and long driving electric vehicles owing to the low specific capacity of conventional intercalation anodes possessing sluggish Li-ion diffusion kinetics. Herein, we demonstrate an unusual pseudocapacitive lithium-ion storage on defective Co3O4 nanosheet anodes for high-performance rechargeable batteries. Cobalt-oxide nanosheets presented here composed of various defects including vacancies, dislocations and grain boundaries. Unique 2D holey microstructure enabled efficient charge transport as well as provided room for volume expansions associated with lithiation-delithiation process. These defective anodes exhibited outstanding pseudocapacitance (up to 87%), reversible capacities (1490 mAh g–1 @ 25 mA g–1), rate capability (592 mAh g–1 @ 30 A g–1), stable cycling (85% after 500 cycles @ 1 A g–1) and columbic efficiency (∼100%). Exceptional Li-ion storage phenomena in defective Co3O4 nanosheets is accredited to the pseudocapacitive nature of conversion reaction resulting from ultrafast Li-ion diffusion through various crystal defects. The demonstrated approach of defect-induced pseudocapacitance can also be protracted for various low-cost and/or eco-friendly transition metal-oxides for next-generation rechargeable batteries.
Tuning the optical properties of 2D monolayer silver-bismuth bromide double perovskite by halide substitution
Authors: Schmitz Fabian , Neisius Raphael , Horn Jonas , Sann Joachim , Schlettwein Derck , Gerhard Marina , Gatti Teresa
Published: February 2022

Silver-bismuth double perovskites are promising replacement materials for lead-based ones in photovoltaic (PV) devices due to the lower toxicity and enhanced stability to environmental factors. In addition, they might even be more suitable for indoor PV, due to the size of their bandgap better matching white LEDs emission. Unfortunately, their optoelectronic performance does not reach that of the lead-based counterparts, because of the indirect nature of the band gap and the high exciton binding energy. One strategy to improve the electronic properties is the dimensional reduction from the 3D to the 2D perovskite structure, which features a direct band gap, as it has been reported for 2D monolayer derivates of Cs2AgBiBr6 obtained by substituting Cs+ cations with bulky alkylammonium cations. However, a similar dimensional reduction also brings to a band gap opening, limiting light absorption in the visible. In this work, we report on the achievement of a bathochromic shift in the absorption features of a butylammonium-based silver-bismuth bromide monolayer double perovskite through doping with iodide and study the optical properties and stability of the resulting thin films in environmental conditions. These species might constitute the starting point to design future sustainable materials to implement as active components in indoor photovoltaic devices used to power the IoT.
Stability, optoelectronic and thermal properties of two-dimensional Janus α-Te2S
Authors: Singh Jaspreet , Jakhar Mukesh , Kumar Ashok
Published: February 2022

Motivated by recent progress in the two-dimensional (2D) materials of group VI elements and their experimental fabrication, we have investigated the stability, optoelectronic and thermal properties of Janus α-Te2S monolayer using first-principles calculations. The phonon dispersion and MD simulations confirm its dynamical and thermal stability. The moderate band gap (∼1.5 eV), ultrahigh carrier mobility (∼103 cm2 V−1 s−1), small exciton binding energy (0.26 eV), broad optical absorption range and charge carrier separation ability due to potential difference (ΔV = 1.07 eV) on two surfaces of Janus α-Te2S monolayer makes it a promising candidate for solar energy conversion. We propose various type-II heterostructures consisting of Janus α-Te2S and other transition metal dichalcogenides for solar cell applications. The calculated power conversion efficiencies of the proposed heterostructures, i.e. α-Te2S/T-PdS2, α-Te2S/BP and α-Te2S/H-MoS2 are ∼21%, ∼19% and 18%, respectively. Also, the ultralow value of lattice thermal conductivity (1.16 W m−1 K−1) of Janus α-Te2S makes it a promising material for the fabrication of next-generation thermal energy conversion devices.
A comparative study of electrical interfaces for tunable piezoelectric vibration energy harvesting
Authors: Morel Adrien , Brenes Alexis , Gibus David , Lefeuvre Elie , Gasnier Pierre , Pillonnet Gaël , Badel Adrien
Published: February 2022

The present work deals with tunable electrical interfaces able to enhance both the harvested power and bandwidth of piezoelectric vibration energy harvesters. The aim of this paper is to propose a general, normalized, and unified performance evaluation (with respect to the harvested power and bandwidth) of the various electrical strategies that can tune the harvester’s frequency response. By mean of a thorough analysis, we demonstrate how such interfaces influence the electromechanical generator response through an electrically-induced damping and an electrically-induced stiffness. The choice of the strategy determines these two electrical quantities, and thus the achievable frequency response of the system. Thereafter, we introduce a collection of graphical and analytical tools to compare and analyze single- and multi-tuning electrical strategies, including a qualitative performance evaluation of existing strategies. Finally, we establish a unified comparison of single- and multiple-tuning strategies which is supported by the definition and evaluation of a new optimization criterion. This comparison reveals which strategy performs best depending on the electromechanical coupling of the piezoelectric harvester and on the losses in the electrical interface. Furthermore, it quantifies the power and bandwidth gain brought by single- and multi-tuning strategies. Such quantitative criterion provides guidance for the choice of a harvesting strategy in any specific applicative case.
Stabilization and control of persistent current magnets using variable inductance
Authors: Brouwer Lucas , Shen Tengming , Norris Ryan , Hafalia Aurelio , Schlueter Ross , Wang Li , Ciston Jim , Ercius Peter , Ji Qing , Mankos Marian , Ophus Colin , Stibor Alexander , Schmid Andreas , Minor Andrew M , Denes Peter
Published: February 2022

Ultra-stable, tunable magnetic fields are desirable for a wide range of applications in medical imaging, electron microscopy, quantum science, and atomic physics. Superconducting magnets operated in persistent current mode, with device current flowing in a closed superconducting loop disconnected from a power source, are a common approach for applications with the most stringent requirements on temporal field stability. We present a method for active control of this persistent current by means of dynamic inductance change within the superconducting circuit. For a first realization of this general technique, we consider a variable superconducting inductor placed in series with the main magnet. The inductor acts as a dynamic flux storage device capable of transferring flux to or from the main magnet through inductance change. This allows for fine and fast adjustments of the persistent current without the use of thermal switches that limit the speed and accuracy of many present-day methods. With first experiments employing this technique, we demonstrate stabilization of a 1.95 T Nb–Ti round lens for electron microscopy against decay resulting from residual losses in the superconducting circuit, and more generally show flexibility for precise control over the magnitude and waveform of the persistent current.
Superconducting fault current limiter (SFCL) for a power electronic circuit: experiment and numerical modelling
Authors: Chen Xiaoyuan , Gou Huayu , Chen Yu , Jiang Shan , Zhang Mingshun , Pang Zhou , Shen Boyang
Published: February 2022

In this article, the superconducting fault current limiter (SFCL) explores its relatively new application: the power electronic circuit. The investigation of this compact-size SFCL involves both the experiments and numerical modelling. A bifilar-shape resistive-type SFCL was used in a DC-DC power conversion circuit, for the purpose of suppressing the overwhelming fault current by 3 different types of faults: the input fault, output fault, and switch fault. The numerical modelling of SFCL used an electromagnetic-thermal coupled finite-element method (FEM) model based on the
H
-formulation. For these 3 types of faults with the 100 ms fault duration, good agreement was found between the experiments and simulations. Both the experiment and modelling method were used to test the SFCL performance with different fault durations (50 ms vs 100 ms). For some severe fault conditions (e.g., higher fault current and longer fault duration) that experiments were difficult or unable to realise, the FEM modelling of SFCL was used to simulate the performance. Overall, the FEM modelling of SFCL can well match the SFCL experiment, and has the advantage of showing more information such as the current distribution and temperature. Both the SFCL experiments and numerical modelling offer new results and novel concepts of SFCL investigation, which can be helpful for the design of future SFCLs and the compact protection schemes for power electronic devices.
Random number generator via hexagonal boron nitride heterostructure
Authors: Hoseini Sani R , Behnia S
Published: February 2022

The nonlinearity is the heart of cryptographic methods which are based on the generation of pseudo-random numbers. In this study, the metal-insulator transition in hexagonal boron nitride (hBN) was investigated as a true random number generator. We have focused on the environmental-dependent behavior of hBN lattices, such as lattice size, impurity types, and applied external voltage on conductivity. The study was carried out based on random matrix theory, with spectral analysis of energy level spectrum and fractal dimension. The results indicate that by increasing the value of the electrical field, the hBN lattice behavior changes from Poisson (regular) to Wigner distribution (chaotic). The study of current-voltage variation has shown the periodic windows of quasi ohmic and the negative differential resistance. The produced electrical current ability as a random number has been examined through generating a dynamical S-box.
Prospects for dark matter signal discovery and model selection via timing information in a low-threshold experiment
Authors: Catena Riccardo , Zema Vanessa
Published: February 2022

In the recent years, many low-threshold dark matter (DM) direct detection experiments have reported the observation of unexplained excesses of events at low energies. Exemplary for these, the experiment CRESST has detected unidentified events below an energy of about 200 eV — a result hampering the detector performance in the search for GeV-scale DM. In this work, we test the impact of nuclear recoil timing information on the potential for DM signal discovery and model selection on a low-threshold experiment limited by the presence of an unidentified background resembling this population of low-energy events. Among the different targets explored by the CRESST collaboration, here we focus on Al2O3, as a sapphire detector was shown to reach an energy threshold as low as 19.7 eV [1]. We test the ability of a low-threshold experiment to discover a signal above a given background, or to reject the spin-independent interaction in favour of a magnetic dipole coupling in terms of p-values. We perform our p-value calculations: 1) taking timing information into account; and 2) assuming that the latter is not available. By comparing the two approaches, we find that under our assumptions timing information has a marginal impact on the potential for DM signal discovery, while provides more significant results for the selection between the two models considered. For the model parameters explored here, we find that the p-value for rejecting spin-independent interactions in favour of a magnetic dipole coupling is about 0.11 when the experimental exposure is 460 g×year and smaller (about 0.06) if timing information is available. The conclusion on the role of timing information remains qualitatively unchanged for exposures as large as 1 kg×5 year. At the same time, our results show that a 90% C.L. rejection of spin-independent interactions in favour of a magnetic dipole coupling is within reach of an upgrade of the CRESST experiment [2].
‘Pushing’ keys through quantum networks and the complexity of search of the true key
Authors: Molotkov S N
Published: February 2022

The question of the transfer of an external independent key through trusted nodes, between which the keys obtained during the quantum key distribution are located, is investigated. It is shown that when pushing external ɛ

K
-secret key through a chain of trusted nodes connecting separate segments with ɛ

i
-secret keys obtained by quantum key distribution, the final matched key between the extreme nodes of the network turns out to be

ε
=

ε
K

+

∑

i
=
1

N
s

ε
i

-secret (where i is the number of the network segment, N

s
is the number of network segments connecting the extreme nodes), provided that the external key is encrypted on the ɛ

i
–secret keys in the one-time pad mode. It is also shown that for any measurements of an eavesdropper providing him with additional information about the keys, the complexity of partial/complete search for an matched key is determined by the secrecy parameter ɛ.
Condensation driven by a quantum phase transition
Authors: Álvarez Miguel Ángel , Reslen Jose
Published: February 2022

The grand canonical thermodynamics of a bosonic system is studied in order to identify the footprint of its own high-density quantum phase transition. The phases displayed by the system at zero temperature establish recognizable patterns at finite temperature that emerged in the proximity of the boundary of the equilibrium diagram. The gapped phase underlines a state of collectivism/condensation at finite temperature in which particles coalesce into the ground state in spite of interacting attractively. The work establishes a framework that allows to study the phenomenon of condensation under the effect of attraction.
Non-destructive evaluation of coatings using terahertz reflection spectroscopy
Authors: Siv Sachin S D , Vijayan Vivek , Kini Rajeev N
Published: February 2022

Terahertz time-domain spectroscopy (THz-TDS) provides a non-contact, non-destructive method for evaluating different materials and their properties. This short review discusses the commonly used numerical models for the non-destructive estimation of thickness, refractive index, surface and interface roughness of paints, thermal barrier coatings, and polymer coatings using THz-TDS in the reflection geometry. To demonstrate the applicability of these models, we used paint layers on metallic substrates and extracted different paraments by fitting the experimental THz-TDS data. We conclude by discussing further steps to improve the efficiency of the fitting procedure used to extract the layer parameters.
Covalent polymer functionalization of graphene/graphene oxide and its application as anticorrosion materials
Authors: Amin Ihsan , Batyrev Erdni , de Vooys Arnoud , van der Weijde Hans , Shiju N Raveendran
Published: February 2022

Research on grapheme-polymer composites as the promising ion barrier materials to tackle the corrosion issue is rapidly developing and attracts interests from both academia and industry. In this minireview, we highlight the covalent functionalization of graphene and its derivatives such as graphene oxide (GO) with polymer brushes, and their application in anticorrosion within the last 3 years. There are some recent excellent reviews published on single layer graphene and graphene-based polymer composites for anticorrosion. However, the covalent functionalization of graphene and GO with polymer brushes for application in anticorrosion has not been addressed in those reviews. In this review, we describe first the current state of the art of covalent functionalization of graphene/GO with polymer brushes. We then discuss the application of pristine graphene as anticorrosion material and its drawbacks which can be overcome by graphene-based polymer composites. Afterwards, we discuss in detail the recent progress and development of covalent polymer functionalized graphene/GO as anticorrosion coatings, reported within the last 3 years. Finally, as perspective, we will briefly summarize the work on composites of polymers with other two-dimensional (2D) materials as anticorrosion coatings. Herein, hexagonal boron nitride, the most studied 2D materials after graphene, and Ti3C2T
x
MXene which is the rising star of 2D transition metal carbide/nitride will be discussed.
Dry tribological properties of M50 bearing steel under different temperatures
Authors: Guo Hao , Duan Haitao , Wang Xingxing , Du Sanming , Zhang Yongzhen , Wang Pei
Published: February 2022

Reducing wear and clarifying relation mechanism are essential to improve the life of engine bearings, so we investigate the influence of ambient temperature on the friction characteristics of M50 steel self-matching pairs under dry friction conditions. As the ambient temperature increases from 30 °C to 500 °C, friction coefficient decreases sharply from 0.78 and tends to be stable around 0.4, while wear rate firstly decreases and then increases. High temperature (More than 300 °C) induces the serious oxidation and softening on the wear surface, causing the main wear mode from abrasive wear to adhesive wear. The oxides include mainly of Fe2O3 and Fe3O4, and minor MoO3 and Cr2O3, which are benefit for forming a continuous tribolayer on the wear surface, thereby improving the friction performance.
Metakaolin-red mud/carbon nanotubes geopolymer nanocomposite: mechanical properties and structural studies
Authors: Ahmadi Hamidreza , Khalaj Gholamreza , Najafi Abolhassan , Abbasi Saloumeh Mesgari , Safari Masumeh
Published: February 2022

In this research, the mechanical properties and structural studies of the geopolymer nanocomposite of metakaolin-red mud/carbon nanotubes were investigated. The geopolymer was designed by using metakaolin and red mud as aluminosilicate sources. Red mud replaced between 10 to 30% of the metakaolin. The mass ratio of the solid material and activator liquid was optimized in 1.5:1. Afterward, 1, 2, and 3 wt% multi-wall carbon nanotubes (MWCNTs) were dispersed in a polycarboxylate-based superplasticizer and were added to the geopolymer, which was mixed homogeneously. Geopolymer nanocomposites were characterized by XRD, FTIR, SEM, compressive and flexural strength measurements. The results indicated that the compressive and flexural strengths of the samples increased with curing time. The addition of red mud decreased the compressive and flexural strength of the geopolymer samples due to less reactivity and presence of a non-reactive impurity in red mud. By adding 2% MWCNTs, the compressive and flexural strengths increased to 37.05% and 36.06%, respectively, owing to the crack-bridging mechanism and filling of the cavities and porosity. FTIR spectra demonstrated the growth of the asymmetric stretching vibrations of T–O–Si (T: Si or Al) at approximately 995.85–1083.55 cm−1, confirming the realization of the geopolymerization process in the structure.
Implementation of apertures in a proton pencil-beam dose algorithm
Authors: Depauw N , Kooy H M , Daartz J , Bussière M , Batin E , Madden T , Williams M , Schueman J , Clasie B M
Published: February 2022

The use of field-specific apertures, routine in scattered or uniform-scanned proton fields, are still a necessity in pencil-beam scanned (PBS) fields to sharpen the penumbral edge at low energies and in high fraction dose application beyond that achievable with small spot size. We describe a model implemented in our clinical pencil-beam algorithm that models the insertion of a shaped aperture, including shapes adapted per energy layer such as may be achieved with a multi-leaf collimator. The model decomposes the spot transport into discrete steps. The first step transport a uniform intensity field of high-resolution sub-pencil-beams at the layer energy through the medium. This transport only considers primary scattering in both the patient and an optional range-shifter. The second step models the aperture areas and edge penumbral transition as a modulation of the uniform intensity. The third step convolves individual steps over the uniform-transported field including the aperture-modified intensities. We also introduce an efficient model based on a Clarkson sector integration for nuclear scattered halo protons. This avoids the explicit modeling of long range halo protons to the detriment of computational efficiency in calculation and optimization. We demonstrate that the aperture effect is primarily due to in-patient and shifter scattering with a small contribution from the apparent beam source position. The model provides insight into the primary physics contributions to the penumbra and the nuclear halo. The model allowed us to fully deploy our PBS capacity at our two-gantry center without which PBS treatments would have been inferior compared to scattered fields with apertures. Finally, Monte Carlo calculations have (nearly) replaced phenomenological pencil-beam models for collimated fields. Phenomenological models do, however, allow exposition of underlying clinical phenomena and closer connection to representative clinical observables.