bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification and characterization of current sheets in collisionless plasma turbulence
Authors: Azizabadi Amirhassan Chatraee , Jain Neeraj , Büchner Jörg
Published: May 2021

Current sheets forming in an ion-kinetic turbulent collisionless plasma are characterized by utilizing the results of two-dimensional hybrid-kinetic numerical simulations (ions treated as kinetic species using particle-in-cell method and electrons treated as mass-less fluid). For this sake, the algorithm, proposed by Zhdankin et al. [Astrophys. J. 771, 124 (2013)] for the identification and characterization of current sheets forming in magnetohydrodynamic plasma turbulence, is extended to current sheets forming in a much noisier kinetic plasma turbulence. Effects of the algorithm parameters on the identification of current sheets in plasma turbulence are analyzed. Based on this analysis, appropriate values of algorithm parameters for the current sheet identification are chosen. Current sheets are statistically characterized in terms of their main properties—the peak current density, the peak current carrier velocity (mainly electrons), the thickness, the length, and also the aspect ratio (length/thickness). Results of the characterization show that the current sheets have a tendency to thin down to below ion inertial length scale until numerical (grid-resolution based) dissipation stops any further thinning. Simulations that include the physics at the electron inertial scales, e.g., hybrid simulations with electron inertia, are required to fully address the current sheet thinning processes and determination of the final thicknesses of current sheets.
Optimization of quantum-dot qubit fabrication via machine learning
Authors: Mei Antonio B. , Milosavljevic Ivan , Simpson Amanda L. , Smetanka Valerie A. , Feeney Colin P. , Seguin Shay M. , Ha Sieu D. , Ha Wonill , Reed Matthew D.
Published: May 2021

Precise nanofabrication represents a critical challenge to developing semiconductor quantum-dot qubits for practical quantum computation. Here, we design and train a convolutional neural network to interpret scanning electron micrographs and quantify qualitative features affecting device functionality. The high-throughput strategy is exemplified by optimizing a model lithographic process within a five-dimensional design space and by demonstrating a robust approach to address lithographic proximity effects. The results emphasize the benefits of machine learning for developing stable processes, shortening development cycles, and enforcing quality control during qubit fabrication.
Lagrangian analysis of enstrophy dynamics in a highly turbulent premixed flame
Authors: Darragh Ryan , Towery Colin A. Z. , Meehan Michael A. , Hamlington Peter E.
Published: May 2021

A Lagrangian analysis approach is used to examine the effects of heat release on the dynamics of the enstrophy during highly turbulent premixed combustion. The analysis is performed using data from a direct numerical simulation of a statistically planar premixed methane–air flame at a Karlovitz number of 100. Through cumulative, conditional, and correlation analyses, we show, consistent with prior studies, that vortex stretching and baroclinic torque both increase enstrophy at these highly turbulent conditions, while viscous transport and dilatation both lead to enstrophy destruction. However, although vortex stretching and viscous transport are individually an order of magnitude greater than all other terms in the enstrophy budget, the cumulative and combined effect of these two terms along Lagrangian trajectories is roughly only twice as large as the combined cumulative effect of dilatation and baroclinic torque. Moreover, trajectories that exhibit an increase in enstrophy through the flame are found to frequently have cumulative contributions from budget terms outside a single standard deviation of the mean contribution, indicating that enstrophy production at such highly turbulent conditions is associated with relatively infrequent but large values of dynamical terms. Lagged correlations further reveal a small but measurable contribution of baroclinic torque in enstrophy production, but these increases are overwhelmed, on average, by concurrent decreases in enstrophy due to viscous transport and dilatation. Taken together, these results provide further understanding of enstrophy dynamics in highly turbulent premixed flames.
Lampert triangle formation and relaxation behavior in doped poly(3,4-ethylenedioxythiophene) devices
Authors: Roy Amit , Mandal Sougata , Menon Reghu
Published: May 2021

The current density–voltage (J–V) characteristics in stainless steel/poly(3,4-ethylenedioxythiophene)/Ag devices show the formation of the complete Lampert triangle (ΔABC) bounded by three limiting curves: Ohmic, trap-limited/filling space charge limited conduction, and trap-free/trap-filled space charge limited conduction. From the analysis of the Lampert triangle, values for carrier density (p0) ∼ 0.72 × 1013/cm3, mobility (μp) ∼ 77.47 × 10−4 cm2/V s, and transit time (tt) ∼ 10−12 s are obtained and also the transition voltages for different conduction mechanisms are estimated. The relaxation processes in bulk and interface are observed to be different from temperature-dependent impedance measurements. Estimated values of relaxation times are interface (τ1) ∼ 10−3 s and bulk (τ2) ∼ 10−6 s. Two parallel RQ (Q: constant phase element) circuits in series are used to fit the impedance data; however, the model varies for data at 110 and 120 K (two parallel CQ circuits in series). Since the samples have doped carriers, the activation energies are low (< 70 meV), and relaxation times follow Arrhenius behavior.
Chemical kinetic mechanisms and scaling of two-dimensional polymers via irreversible solution-phase reactions
Authors: Zhang Ge , Zeng Yuwen , Gordiichuk Pavlo , Strano Michael S.
Published: May 2021

Two-dimensional (2D) polymers are extended networks of multi-functional repeating units that are covalently linked together but confined to a single plane. The past decade has witnessed a surge in interest and effort toward producing and utilizing 2D polymers. However, facile synthesis schemes suitable for mass production are yet to be realized. In addition, unifying theories to describe the 2D polymerization process, such as those for linear polymers, have not yet been established. Herein, we perform a chemical kinetic simulation to study the recent synthesis of 2D polymers in homogeneous solution with irreversible chemistry. We show that reaction sites for polymerization in 2D always scale unfavorably compared to 3D, growing as molecular weight to the 1/2 power vs 2/3 power for 3D. However, certain mechanisms can effectively suppress out-of-plane defect formation and subsequent 3D growth. We consider two such mechanisms, which we call bond-planarity and templated autocatalysis. In the first, although single bonds can easily rotate out-of-plane to render polymerization in 3D, some double-bond linkages prefer a planar configuration. In the second mechanism, stacked 2D plates may act as van der Waals templates for each other to enhance growth, which leads to an autocatalysis. When linkage reactions possess a 1000:1 selectivity (γ) for staying in plane vs rotating, solution-synthesized 2D polymers can have comparable size and yield with those synthesized from confined polymerization on a surface. Autocatalysis could achieve similar effects when self-templating accelerates 2D growth by a factor β of 106. A combined strategy relaxes the requirement of both mechanisms by over one order of magnitude. We map the dependence of molecular weight and yield for the 2D polymer on the reaction parameters, allowing experimental results to be used to estimate β and γ. Our calculations show for the first time from theory the feasibility of producing two-dimensional polymers from irreversible polymerization in solution.
Solution-processed solar-charging power units made of organic photovoltaic modules and asymmetric super-capacitors
Authors: Jin Yingzhi , Sun Lulu , Qin Leiqiang , Liu Yanfeng , Li Zaifang , Zhou Yinhua , Zhang Fengling
Published: May 2021

Organic photovoltaics with the properties of flexibility, portability, and printability are ideal candidates for low-power-consumption electronics such as the Internet of Things under indoor light conditions. In this work, an all solution-processed integrated photocapacitor (IPC) consisting of an organic photovoltaic module (OPVM) and an asymmetric super-capacitor (ASC) is demonstrated. The OPVM poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)benzo[1, 2-c:4,5-c′]dithiophene-4,8-dione)] (PBDB-T) : 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′d′]-s-indaceno[1,2-b:5,6-b-]-dithiophene (ITIC) with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the top electrode delivers a high power conversion efficiency of 6.7% with a voltage of 4.3 V (1 Sun). The ASC based on PEDOT:PSS and Ti3C2Tx electrodes shows a wide operation window of 1.5 V in the aqueous electrolyte with a high energy density of 28.7 μW h cm−2. Consequently, the IPC achieves a high output voltage of 3 V and outstanding overall efficiency of 6.0% (45 000 lx), which shows excellent stability as the solar-charging power unit under room light (500 lx). Synergizing energy harvest and storage in a solution-processed robust, lightweight, low-cost organic IPC enables this solar-charging power unit wide potential applications in low-power-consumption portable electronics.
Internal solitary waves induced deep-water nepheloid layers and seafloor geomorphic changes on the continental slope of the northern South China Sea
Authors: Tian Zhuangcai , Jia Yonggang , Chen Jiangxin , Liu J. Paul , Zhang Shaotong , Ji Chunsheng , Liu Xiaolei , Shan Hongxian , Shi Xuefa , Tian Jiwei
Published: May 2021

Internal solitary waves (ISWs) can cause strong seafloor sediment resuspension and induce nepheloid layers in both shallow and deep-water environments. However, the roles of ISWs in the >1000 m deep sea sediment resuspension and seafloor geomorphic changes are still unclear. To answer the above question, in the Dongsha area of the northern South China Sea, we measured suspended particulate matter along with a section covering the entire continental slope between 300 and 2000 m water depths, together with high-resolution multibeam bathymetric data for examining geomorphic changes. The results indicate that, on the upper slope with water depth <700 m, seafloor sediments were heavily disturbed and resuspended. We find that ISWs could suspend seabed sediments and shape a bedform at water depths ≲1000 m. The maximum water depth of sediment resuspension by ISWs measured is found as deep as 1500 m. The distribution pattern of the seafloor surface sediments on the east of the Dongsha continental slope (fine and silty sand in <700 m water depth, clayey silt between 700 and 1500 m, and silty clay > 1500 m) also indicates that they are mainly controlled and impacted by ISWs. The wave refraction theory could be applied to the upper slope, but sediment resuspension is related to the seabed topography on the lower slope. Our study shows that the suspension and transport of sediments induced by episodic ISWs on the Dongsha slope of the northern South China Sea could shape the bedform and affect the sedimentary seabed geomorphology. This research will help explain the impacts of the ISWs on the deep-water sediment resuspension and seafloor geopmorphic changes along with the continental slope in the margin sea.
Experimental investigation of the wake dynamics for a NACA0012 airfoil with a cut-in serrated trailing-edge
Authors: Hasheminasab S. M. , Karimian S. M. H. , Noori S. , Saeedi M. , Morton C.
Published: May 2021

An experimental investigation of the unsteady dynamics in the wake of a NACA0012 (National Advisory Committee for Aeronautics) airfoil with a narrow-angle cut-in serrated trailing-edge is presented. Time-resolved planar particle image velocimetry (PIV) has been performed in the wake region of the airfoil both with and without serrations at a Reynolds number of 78 000. The boundary layers on both sides of the airfoil surface are tripped and the angle of attack is held fixed at zero. Spectral analysis of the PIV results shows that the trailing-edge serrations are linked to increased velocity fluctuations in the wake region which are centered on a non-dimensional frequency range of fc/U∞≈3−5. Proper orthogonal decomposition (POD) is utilized to analyze the spatiotemporal characteristics of the most dominant structures in the wake. Three POD mode pairs identified in the serrated airfoil wake flow are described in detail in two different PIV measurement planes passing through the tip and root of the serrations. Overall, the serrations substantially increase the turbulent kinetic energy in the wake and concentrate this energy within the three identified mode pairs. Spectral analysis of the temporal coefficient signals pertaining to the three mode pairs shows energy concentrated within the frequency band of increased velocity fluctuations identified in the wake region. POD-based reconstruction unfolded a von Kármán-like vortex shedding from the truncated part of the airfoil with fc/U∞≈3.7, which is primarily v-fluctuation driven, convecting through the domain at close to 90% of the free stream velocity.
Generalized impurity pinch in partially magnetized multi-ion plasma
Authors: Mlodik M. E. , Kolmes E. J. , Ochs I. E. , Fisch N. J.
Published: May 2021

In a two-ion-species plasma with disparate ion masses, heavy ions tend to concentrate in the low-temperature region of collisionally magnetized plasma and in the high-temperature region of collisionally unmagnetized plasma, respectively. Moreover, collisional magnetization can be determined as the ratio of the light ion gyrofrequency to the collision frequency of light and heavy ion species, and the behavior of this effect in the intermediate regime of partially magnetized plasma is predominantly dependent on this Hall parameter. Multi-ion cross-field transport has been described before in the collisionally magnetized plasma regime, and generalized pinch relations, which describe densities of ion species in equilibrium in that plasma, are found in the literature. In this paper, the role of collisional magnetization and Larmor magnetization in multi-ion collisional transport is clarified, and generalized pinch relations are extended to the partially magnetized regime in which the ion Hall parameter may be small, as long as electrons remain collisionally magnetized. Equilibrium ion density profiles have the same dependence on external forces and on each other regardless of collisional magnetization of ions. The expansion of the range of validity of multi-ion collisional transport models makes them applicable to a wider range of laboratory plasma conditions. In particular, ion density profiles evolve sufficiently fast for radial impurity transport to be observable around stagnation on MagLIF, leading to expulsion of heavy ion impurities from the hotspot as long as plasma becomes sufficiently collisionally magnetized during the implosion.
Dielectric barrier discharges in airflow around a circular cylinder
Authors: Tang Miao , Tang Jingfeng , Zhou Desheng , Yu Daren
Published: May 2021

The influence of airflow on the dielectric barrier discharge is a widely investigated topic for its extensive applications. In this paper, the discharge pattern and motion law of discharge spots under Karman's vortex street on atmospheric pressure are experimentally investigated by constructing the airflow around a circular cylinder. It is found that the discharge filament composed of the movement trajectory of the discharge spots has a good corresponding relationship with the streamline. When the Reynolds number is increased, the flow field at the rear of the cylinder changes from laminar to vortex. The discharge patterns at an appropriate exposure time reflect the topological structure of the wake flow, which changed with the Reynolds number.
Voltage-controlled superparamagnetic ensembles for low-power reservoir computing
Authors: Welbourne A. , Levy A. L. R. , Ellis M. O. A. , Chen H. , Thompson M. J. , Vasilaki E. , Allwood D. A. , Hayward T. J.
Published: May 2021

We propose thermally driven, voltage-controlled superparamagnetic ensembles as low-energy platforms for hardware-based reservoir computing. In the proposed devices, thermal noise is used to drive the ensembles' magnetization dynamics, while control of their net magnetization states is provided by strain-mediated voltage inputs. Using an ensemble of CoFeB nanodots as an example, we use analytical models and micromagnetic simulations to demonstrate how such a device can function as a reservoir and perform two benchmark machine learning tasks (spoken digit recognition and chaotic time series prediction) with competitive performance. Our results indicate robust performance on timescales from microseconds to milliseconds, potentially allowing such a reservoir to be tuned to perform a wide range of real-time tasks, from decision making in driverless cars (fast) to speech recognition (slow). The low energy consumption expected for such a device makes it an ideal candidate for use in edge computing applications that require low latency and power.
Temperature dependent size effects on crystal growth of nanorods revealed by molecular dynamics simulations
Authors: Wang Risheng , Wang Feifei , Yang Gongji , Wang Mingxu , Kong Lingti , Li Jinfu
Published: May 2021

Nano metallic materials are promising candidates in many engineering applications, whereas their thermal stability is generally of great concern. In this study, molecular dynamics simulations were performed to study the crystal growth process of CuZr nanorods with different diameters. An appreciable size effect was observed in the crystal growth rates. However, the trend of size dependence could be reversed by changing the temperature. For temperatures above 925 K, nanorods of smaller diameters grow slower than those with larger diameters, while for temperatures below 925 K, smaller nanorods grow faster. It turns out that the temperature dependent size effect originates from the competition between the thermodynamic and kinetic factors. Atoms in the surficial region of the nanorods have higher mobility while lower thermodynamic driving force for growth than those in the interior. Under different temperatures, the overwhelming factor varies, leading to the temperature dependent size effect. A phenomenological model was proposed accordingly to describe the size dependence, which is found to work well under all temperatures explored.
Directly grown crystalline gallium phosphide on sapphire for nonlinear all-dielectric nanophotonics
Authors: Khmelevskaia D. , Markina D. I. , Fedorov V. V. , Ermolaev G. A. , Arsenin A. V. , Volkov V. S. , Goltaev A. S. , Zadiranov Yu. M. , Tzibizov I. A. , Pushkarev A. P. , Samusev A. K. , Shcherbakov A. A. , Belov P. A. , Mukhin I. S. , Makarov S. V.
Published: May 2021

Efficient second harmonic generation (SHG) in nanophotonic designs based on all-dielectric nanostructures demands materials with large values of the quadratic nonlinear susceptibility, low dissipative losses, and high refractive index. One of the best materials meeting all these parameters is gallium phosphide (GaP). However, second-order nonlinearity requires high crystallinity and morphology quality of the GaP layer grown for further lithographic processing. Here we develop a method to fabricate high-quality crystalline GaP metasurfaces, which demonstrate pronounced linear and nonlinear optical properties. Direct growth of a GaP layer on a sapphire substrate tackles the previous problem of wafer bonding, because of high optical contrast between fabricated resonant nanoparticles and the substrate. As a result, the fabricated GaP metasurface supports bound state in continuum mode with an experimental quality factor around 100 yielding a strong enhancement of SHG in narrow spectral range. We believe that the developed approach will become a versatile platform for nonlinear all-dielectric nanophotonics.
Noninvasive method to measure the electron temperature in radio frequency capacitively coupled plasmas
Authors: Lee Hyo-Chang , Chung C.-W. , Lee M. H. , Kim J. H.
Published: May 2021

The electron temperature Te is a key plasma parameter in both industrial plasma processes and fundamental laboratory research. A noninvasive method to measure Te in current and next-generation semiconductor plasma processes is urgently required for fine-tuning the processing result and virtual metrology based on the plasma monitoring. In this Letter, we propose a noninvasive method for obtaining Te in radio frequency capacitively coupled plasma (CCP) by measuring the floating potential and substrate potential. The Te obtained using this simple method was compared with the results measured by a floating Langmuir probe in both pure Ar and Ar/He mixture CCPs, and they showed good agreement.
Impurity incorporation and diffusion from regrowth interfaces in N-polar GaN photocathodes and the impact on quantum efficiency
Authors: Rocco Emma , Mahaboob Isra , Hogan Kasey , Meyers Vincent , McEwen Benjamin , Bell L. D. , Shahedipour-Sandvik F.
Published: May 2021

We investigate the mechanisms of growth interruption mediated interfacial impurity diffusion in N-polar GaN, and through this understanding, we offer an approach toward achieving high quantum efficiency III-nitride photocathode devices. N-polar photocathode structures consisting of a p-GaN active layer and a thin unintentionally doped GaN (u-GaN) cap layer were grown on an N-polar u-GaN template with varied growth interruptions at interfaces. Unintentionally incorporated oxygen and silicon impurity spikes at regrowth interfaces were measured by secondary ion mass spectrometry. Pipe and bulk diffusion of the oxygen impurity is observed from the regrowth interfaces when the overgrown layer required higher temperature growth, whereas only bulk diffusion is seen otherwise. Furthermore, the proximity of regrowth interfaces to the surface is observed to impact the diffusivity of oxygen. Growth interruption between the p-GaN active layer and cap layer resulted in a low quantum efficiency of 0.27%, while uninterrupted growth of the p-GaN/u-GaN cap photocathode achieved a quantum efficiency of 10.79%. We attribute the low quantum efficiency of the interrupted cap photocathode to the high density of oxygen within the active region of the device. Understanding of impurity incorporation at regrowth interfaces, dominating driving mechanisms behind diffusion of these species, and their impact on material properties are critical elements in designing high performing devices.
Review on the operation of wearable sensors through body heat harvesting
based on thermoelectric devices
Authors: Khan Salman , Kim Jiyong , Acharya Somnath , Kim Woochul
Published: May 2021

The development of wearable sensors is currently receiving considerable attention owing to their potential usefulness in real-time health monitoring during ongoing assessments of personal health. The generation of thermoelectric power from body heat offers an attractive solution to supply power to these wearable devices. This review highlights the successes of flexible thermoelectric generators that have been achieved to date and also alludes to the remaining problems regarding the operation of wearable sensors based on power generated from harvested body heat. Specifically, appropriate simulation based on human thermoregulatory models, flexible heat sinks, electronics, and energy storage devices are relevant because their development would have to occur alongside that of wearable sensors to enable the implementation of these sensors in practice.
Crystal growth in deeply undercooled Ni50Al50: Signature of the ordering sequence at the interface
Authors: Yang Qianjin , Liu Huashan , Peng Hailong
Published: May 2021

Crystal growth of the intermetallic alloy, Ni50Al50, is investigated by molecular dynamics simulations with two different interatomic potentials. The calculated growth rate can be captured by the Wilson–Frenkel or Broughton–Gilmer–Jackson model at small undercoolings but deviates from the theory at deep undercoolings. Failure of the theory is found to be correlated with the dynamic processes that emerged at the interface, but not apparently with the static interface structure. The chemical segregation of Ni and Al atoms occurs before the geometrical ordering upon crystallization at small undercoolings. In contrast, the geometrical ordering precedes the chemical one at deep undercoolings. These two ordering processes show a collapsed time evolution at the crossover temperature consistent with the onset of the theoretical deviation. We rationalize the delayed chemical segregation behavior by the collective atomic motion, which is characterized by the super-Arrhenius transition of the temperature-dependent diffusivity and structural relaxation time at the crossover point.
High-throughput bend-strengths of ultra-small polysilicon MEMS components
Authors: Cook Robert F. , Boyce Brad L. , Friedman Lawrence H. , DelRio Frank W.
Published: May 2021

The strength distribution of polysilicon bend specimens, approximately 10 μm in size, is measured using a high-throughput microelectromechanical system fabrication and testing method. The distribution is predicted from reference tests on tensile specimens and finite element analysis of the bend specimen geometry incorporated into a stochastic extreme-value strength framework. Agreement between experiment and prediction suggests that the ultra-small specimens may be at the limit of extreme-value scaling and contain only one strength-controlling flaw/specimen.
Conditional and unconditional second-order structure functions in bubbly channel flows of power-law fluids
Authors: Trautner E. , Klein M. , Bräuer F. , Hasslberger J.
Published: May 2021

The influence of non-Newtonian fluid behavior and the Eötvös number on conditional and unconditional second-order structure functions of bubbly channel flows has been investigated by conducting a series of direct numerical simulations at a friction Reynolds number of 127.3. Two Eötvös numbers have been considered (Eo = 0.3125 and Eo = 3.75) together with three different power-law indexes representing shear-thinning (n = 0.7), Newtonian (n = 1.0), and shear-thickening (n = 1.3) fluid behavior. The scaling of the second-order structure functions (SFs) can be translated into an inertial range scaling of the turbulent kinetic energy spectrum. However, because of the discontinuous character of the fluid properties in bubbly flows, SFs are more easily accessible than turbulence spectra, which are based on Fourier transform. It has been found that the different parameters (i.e., Eo, n) have an influence on the energy content as well as the peak location of the compensated second-order SFs (i.e., the dimensions of the large scales). However, after appropriate scaling, the curves nearly collapse. To confirm and further explain the above findings, directional length scales have been evaluated and discussed in detail. Finally, the anisotropy of the Reynolds stress tensor and dissipation tensor has been analyzed in terms of the Lumley triangle, showing that bubbly channel flows are less isotropic than their single-phase counterpart, although they are more homogeneous in the channel center. While the dissipation tensor is slightly more isotropic than the Reynolds stress tensor in the bulk region of the channel flow, overall, a very similar behavior is observed.
Effect of ionic liquids in carbon nanotube bundles on CO2, H2S, and N2 separation from CH4: A computational study
Authors: Barzegar Behnoush , Feyzi Farzaneh
Published: May 2021

Carbon nanotube (CNT) bundles are being explored as a support structure for four ionic liquids (ILs) in gas separation. Grand canonical Monte Carlo simulations were performed to investigate the CO2/CH4, H2S/CH4, and N2/CH4 separation performance in CNT bundles and CNT-supported ILs (CNT-ILs) as a function of pressure and IL loading. The results show that by adding ILs to the CNT bundles, the gas separation performance can be significantly increased. Increasing the number of IL molecules in the composites increases the separation performance. Such a phenomenon is more evident for the CO2/CH4 mixture in comparison to H2S/CH4 and N2/CH4. Calculations of isosteric heat of adsorption and selectivities in gas mixtures as a function of pressure show promising gas separation performance for CNT-ILs. Due to the excellent mechanical properties of CNTs, it has been shown that this structure may be used as a strong mechanical support for structures containing ILs with excellent CO2/CH4 separation performance.
Friction reduction in a nanochannel with grafted poly(N-isopropylacrylamide) oligomers: A molecular dynamics study
Authors: Saleki O. , Moosavi A. , Hannani S. K.
Published: May 2021

Superhydrophobic surfaces have been used for reducing friction in micro- and nanochannels. In the present work, water flow between two carbon walls with nanostructures made of poly(N-isopropylacrylamide) via the molecular dynamics method has been studied. The structure of this polymer can change based on the temperature of the environment, so that by increasing the temperature the structure becomes hydrophobic. This property has been studied and the effect of multiple factors on the slip length is presented. The effects of the number of monomers in the polymer, the distance between the polymers, and the temperature on the flow field are investigated. The results reveal that the slip length and the flow rate increase with the temperature but both have a maximum with respect to the distance between the polymers and the number of monomers. For different temperatures considered in the study, the minimum friction occurs when the number of monomers and the distance are equal to 30 and 80, respectively. In this condition, the slip length increases by 180% and the flow rate rises by 200%. We also study the effect of air fraction in the fluid. The results indicate that by increasing the air fraction to 30%, the slip length and the flow rate increase by 250% and 310%, respectively.
Higher order curvature corrections to the field emission current density
Authors: Biswas Debabrata , Ramachandran Rajasree
Published: May 2021

A simple expression for the Gamow factor is obtained using a second-order curvature-corrected tunneling potential. Our results show that it approximates accurately the “exact-WKB” transmission coefficient obtained by numerically integrating over the tunneling region to obtain the Gamow factor. The average difference in current density using the respective transmission coefficients is about 1.5%, across a range of work functions ϕ∈[3−5.5] eV, Fermi energy EF∈[5−10] eV, local electric fields El∈[3−9] V/nm, and radius of curvature R≥5 nm. An easy-to-use correction factor λP is also provided to approximately map the “exact-WKB” current density to the “exact” current density in terms of EF/ϕ. The average error on using λP is found to be around 3.5%. This is a vast improvement over the average error of 15% when λP=1. Finally, an analytical expression for the curvature-corrected current density is obtained using the Gamow factor. It is found to compare well with the “exact-WKB” current density even at small values of local electric field and the radius of curvature.
Coupling between slow waves and sharp-wave ripples engages distributed neural activity during sleep in humans
Authors: Skelin Ivan , Zhang Haoxin , Zheng Jie , Ma Shiting , Mander Bryce A. , Kim McManus Olivia , Vadera Sumeet , Knight Robert T. , McNaughton Bruce L. , Lin Jack J.
Published: May 2021

Significance

Hippocampal sharp wave/ripples (SWRs) are implicated in binding distributed subcortical/cortical neuronal populations during sleep, supporting hippocampal-dependent memory consolidation. We assessed the activation and functional interactions between distributed populations during SWRs using intracranial electrophysiological recordings from human epileptic patients. Consistent phase relation between the hippocampal SWRs and local subcortical/cortical slow-wave activity (SWA) or spindles was a strong predictor of local neuronal activation during SWRs. In addition, individual SWR amplitude and SWA phase difference between the cortical sites during SWRs predicted the functional coupling between the distant cortical populations. Our findings suggest the SWR–SWA coupling as a mechanism for selecting and organizing the distributed populations for participation in global memory consolidation.
Odor-driven face-like categorization in the human infant brain
Authors: Rekow Diane , Baudouin Jean-Yves , Poncet Fanny , Damon Fabrice , Durand Karine , Schaal Benoist , Rossion Bruno , Leleu Arnaud
Published: May 2021

Significance

The adult human brain is organized in unimodal regions responding selectively to categories of environmental sensory stimuli. Here, we document the origin of category-selective visual brain responses in infancy, demonstrating the key contribution of other senses. Visual categorization is recorded neurally in 4-mo-old infants presented with rapid trains of natural images of nonface objects. A concurrent maternal odor initiates the neural response to periodically presented face-like objects categorized as faces in the specialized right hemisphere. This observation provides invaluable clues to understand how the developing visual system builds upon multisensory experience to start categorizing ambiguous and complex unimodal sensory inputs.
The SHREAD gene therapy platform for paracrine delivery improves tumor localization and intratumoral effects of a clinical antibody
Authors: Smith Sheena N. , Schubert Rajib , Simic Branko , Brücher Dominik , Schmid Markus , Kirk Niels , Freitag Patrick C. , Gradinaru Viviana , Plückthun Andreas
Published: May 2021

Significance

A challenge in cancer therapy is delivering high, consistent levels of therapeutics to tumors. Protein-based therapeutics (e.g., antibodies) are typically delivered intravenously and require multiple doses to get sufficient levels to traffic into tumors to exert an effect. Yet healthy tissues are also exposed to similar drug levels, which can lead to significant side effects. This study uses sophisticated three-dimensional imaging of transparent tumors to characterize a versatile gene therapy platform using adenovirus that solves this problem by producing drugs directly in the tumor. This approach increases the tumor-to-bloodstream level of a model antibody 1,800-fold in comparison to direct administration. Thus, this system could allow for the local production of highly potent drugs with greatly reduced risk of systemic toxicities.
Coastal eutrophication drives acidification, oxygen loss, and ecosystem change in a major oceanic upwelling system
Authors: Kessouri Faycal , McWilliams James C. , Bianchi Daniele , Sutula Martha , Renault Lionel , Deutsch Curtis , Feely Richard A. , McLaughlin Karen , Ho Minna , Howard Evan M. , Bednaršek Nina , Damien Pierre , Molemaker Jeroen , Weisberg Stephen B.
Published: May 2021

Significance

We conduct a modeling study of the effects of enhanced coastal nutrient export from human activities on the carbon, nitrogen, and oxygen cycles of the Southern California Bight, in the context of emerging global climate change. The modeling approach used is innovative in the breadth of its scope, and simulations are generally consistent with local measurements. The human effects on the regional ecosystem from coastal nitrogen inputs of 23 million people are substantial, leading to significant increases in the photosynthesis and biomass of phytoplankton and increased oxygen loss and acidification of the water column. These changes are likely to compress habitat for a variety of marine organisms, with cascading ecological effects and implications for marine resources and water-quality management.
An additive algorithm for origami design
Authors: Dudte Levi H. , Choi Gary P. T. , Mahadevan L.
Published: May 2021

Significance

Origami, the art of paper folding, is an emerging platform for mechanical metamaterials. Prior work on the design of origami-based structures has focused on simple geometric constructions for limited spaces of origami typologies or global constrained optimization problems that are difficult to solve. Here, we reverse the mathematical, computational, and physical paradigm of origami design by proposing a simple local marching approach that leads to a constructive theorem on the geometry of compatible growth directions at the boundary of a given folded seed. We show how this discovery yields a simple algorithm for the additive design of all developable quadrilateral surfaces, enabling the design of novel foldable metastructures from flat sheets at any scale.
On the evolution of chaperones and cochaperones and the expansion of proteomes across the Tree of Life
Authors: Rebeaud Mathieu E. , Mallik Saurav , Goloubinoff Pierre , Tawfik Dan S.
Published: May 2021

Significance

Across the Tree of Life, life’s phenotypic diversity has been accompanied by a massive expansion of the protein universe. Compared with simple prokaryotes that harbor thousands of proteins, plants and animals harbor hundreds of thousands of proteins that are also longer, multidomain, and comprise a variety of folds and fold combinations, repeated segments, and beta-rich architectures that make them prone to misfolding and aggregation. Surprisingly, the relative representation of core chaperones, those dedicated to maintaining the folding quality of these increasingly complex proteomes, did not change from prokaryotic to mammalian genomes. To reconcile the expanding proteomes, core chaperones have rather increased in cellular abundance and evolved to function cooperatively as a network, combined with their supporting workforce, the cochaperones.
A synthetic C4 shuttle via the β-hydroxyaspartate cycle in C3 plants
Authors: Roell Marc-Sven , Schada von Borzyskowski Lennart , Westhoff Philipp , Plett Anastasija , Paczia Nicole , Claus Peter , Schlueter Urte , Erb Tobias J. , Weber Andreas P.M.
Published: May 2021

Significance

Photorespiration is essential for photosynthesis in an oxygen-containing atmosphere. By mass flow, photorespiration is exceeded only by photosynthetic carbon assimilation. Photorespiration, initiated by the oxygenation reaction of Rubisco, is a major constraint on the photosynthetic efficiency of C3 plants and consequently on crop yield. Mitigating the negative effects of photorespiration holds potential for yield increases and contributes to achieving food and energy security for a growing population. This work presents a synthetic bypass to natural photorespiration (i.e., the conversion of photorespiratory glycolate into a C4 compound via a recently discovered microbial glycolate assimilation pathway, the β-hydroxyaspartate cycle [BHAC]). Simultaneous expression of four enzymes of microbial origin in the land plant modelArabidopsis thalianaenables efficient glycolate conversion into BHAC products.
Microchemomechanical devices using DNA hybridization
Authors: Zhu Guolong , Hannel Mark , Sha Ruojie , Zhou Feng , Ben Zion Matan Yah , Zhang Yin , Bishop Kyle , Grier David , Seeman Nadrian , Chaikin Paul
Published: May 2021

Significance

With simple DNA origami lever arms arranged in hinges and accordion structures, we amplify the nanometer displacements from DNA hairpin zippers to 4-μm motion, easily observable and quantified in real space and real time with conventional optical microscopy. Mechanically pulling a bead tethered on the accordion end, we measure high-energy recovery and retraction speeds up to 50 μm/s. On longer time scales, we have also opened and closed the hinges with light and heat. DNA nanotechnology, and particularly DNA origami, combined with colloids and emulsions can provide powerful architectures. The present study is a step toward activating such colloidal/cellular scale devices using DNA as a power source/fuel. We envision artificial active flagella, cilia, micropumps, and other cellular scale devices.
Background-free dual-mode optical and13C magnetic resonance imaging in diamond particles
Authors: Lv Xudong , Walton Jeffrey H. , Druga Emanuel , Wang Fei , Aguilar Alessandra , McKnelly Tommy , Nazaryan Raffi , Liu Fanglin Linda , Wu Lan , Shenderova Olga , Vigneron Daniel B. , Meriles Carlos A. , Reimer Jeffrey A. , Pines Alexander , Ajoy Ashok
Published: May 2021

Significance

We report on progress toward combining magnetic resonance imaging (MRI) and optical imaging in diamond microparticles. Our approach relies on the nitrogen vacancy (NV) center-driven optical nuclear hyperpolarizability in diamond particles, that renders them “bright” in MRI while simultaneously fluorescing optically. Both imaging modes allow suppression of background signals. We elucidate how such “dual-mode” imaging can perform better than either modes taken separately, leveraging relative strengths of optics and MRI with respect to resolution and imaging in scattering media. Finally, we propose a protocol for accelerated imaging that exploits the Fourier conjugacy in images obtained via optics and MRI. Our work suggests methods to combine optical and RF imaging in classes of deployable nanoparticles.
Critical slowing down suggests that the western Greenland Ice Sheet is close to a tipping point
Authors: Boers Niklas , Rypdal Martin
Published: May 2021

Significance

It has been suggested that, in response to anthropogenic global warming, the Greenland Ice Sheet may reach a tipping point beyond which its current configuration would become unstable. A crucial nonlinear mechanism for the existence of this tipping point is the positive melt-elevation feedback: Melting reduces ice sheet height, exposing the ice sheet surface to warmer temperatures, which further accelerates melting. We reveal early-warning signals for a forthcoming critical transition from ice-core-derived height reconstructions and infer that the western Greenland Ice Sheet has been losing stability in response to rising temperatures. We show that the melt-elevation feedback is likely to be responsible for the observed destabilization. Our results suggest substantially enhanced melting in the near future.
Gut microbiome contributions to altered metabolism in a pig model of undernutrition
Authors: Chang Hao-Wei , McNulty Nathan P. , Hibberd Matthew C. , O’Donnell David , Cheng Jiye , Lombard Vincent , Henrissat Bernard , Ilkayeva Olga , Muehlbauer Michael J. , Newgard Christopher B. , Barratt Michael J. , Lin Xi , Odle Jack , Gordon Jeffrey I.
Published: May 2021

Significance

Employing an intergenerational model of diet restriction (DR) that reduces weight gain, we identify differences in carbohydrate metabolic enzyme gene content of DR versus full-fed (FF) pig gut microbiomes as animals experienced a phased-feeding program administered to farm-raised pigs during their growth cycle. Gnotobiotic mice harboring DR or FF pig microbiomes and fed a corn/soy-dominated pig diet disclosed that the DR microbiome has reduced capacity to produce butyrate, a key diet-derived energy source, and alters hepatic energy metabolism. Combining studies of farm animal microbiome development with functional assays of their microbiomes in gnotobiotic mice should help generate husbandry recommendations for promoting healthy growth of animals during this time of increasing food insecurity and mandates to eliminate subtherapeutic antibiotics for growth-promotion.
Encapsulation of ribozymes inside model protocells leads to faster evolutionary adaptation
Authors: Lai Yei-Chen , Liu Ziwei , Chen Irene A.
Published: May 2021

Significance

Organization into cells is believed to have been crucial for the emergence of life, as the cell membrane would prevent loss of biochemical contents and define an evolutionary entity. RNA is a candidate primordial biomolecule, as it can encode and transmit information and also fold into catalytically active structures. Biomolecules are known to behave differently inside cells compared to bulk solution due to differences in the biophysical environment. However, the consequences of encapsulation on early evolution are unknown. We found that, in a lipid-rich environment, ribozyme encapsulation would promote greater activity and faster adaptation. Better RNA catalysts experience greater gains in a “rich-get-richer” phenomenon. Rather than acting as passive containers, protocells would provide functional and evolutionary benefits to encapsulated contents.
Permafrost carbon feedbacks threaten global climate goals
Authors: Natali Susan M. , Holdren John P. , Rogers Brendan M. , Treharne Rachael , Duffy Philip B. , Pomerance Rafe , MacDonald Erin
Published: May 2021

Rapid Arctic warming has intensified northern wildfires and is thawing carbon-rich permafrost. Carbon emissions from permafrost thaw and Arctic wildfires, which are not fully accounted for in global emissions budgets, will greatly reduce the amount of greenhouse gases that humans can emit to remain below 1.5 °C or 2 °C. The Paris Agreement provides ongoing opportunities to increase ambition to reduce society’s greenhouse gas emissions, which will also reduce emissions from thawing permafrost. In December 2020, more than 70 countries announced more ambitious nationally determined contributions as part of their Paris Agreement commitments; however, the carbon budgets that informed these commitments were incomplete, as they do not fully account for Arctic feedbacks. There is an urgent need to incorporate the latest science on carbon emissions from permafrost thaw and northern wildfires into international consideration of how much more aggressively societal emissions must be reduced to address the global climate crisis.
Accidental synthesis of a previously unknown quasicrystal in the first atomic bomb test
Authors: Bindi Luca , Kolb William , Eby G. Nelson , Asimow Paul D. , Wallace Terry C. , Steinhardt Paul J.
Published: May 2021

Significance

This article reports the discovery of a heretofore unknown icosahedral quasicrystal created by the detonation of the first nuclear device at Alamogordo, NM, on 16 July 1945 (the Trinity test). Like all quasicrystals, the new example violates crystallographic symmetry rules that apply to ordinary (periodic) crystals. It was found in a sample of red trinitite, a combination of glass fused from natural sand and anthropogenic copper from transmission lines used during the test. The new quasicrystal is the oldest extant anthropogenic quasicrystal known, whose place and moment of origin are known from the historic records of the Trinity test. The thermodynamic/shock conditions that formed it are roughly comparable to those that formed natural quasicrystals recently found in meteorites.
HIV envelope tail truncation confers resistance to SERINC5 restriction
Authors: Haider Tafhima , Snetkov Xenia , Jolly Clare
Published: May 2021

Significance

SERINCs and IFITMs are potent lentiviral restriction factors that inhibit infection by blocking viral entry into cells. Specifically, SERINCs inhibit viral fusion by targeting the envelope glycoprotein (Env) by a mechanism that remains incompletely understood. Here, we report that truncation of the Env cytoplasmic tail (CT) of HIV-1 and HIV-2 confers complete resistance to SERINC and IFITM restriction. Notably, while the EnvCT of HIV-1 is necessary for viral replication in T cells, HIV-2 does not require the EnvCT. Our data suggest a mechanism by which human lentiviruses can evade restriction that is mediated by the EnvCT but reveal key differences in the likely fitness cost imposed by this on pandemic HIV-1 and nonpandemic HIV-2.