bluuebunny/crossref_metadata_2025 huggingface dataset:
Tunable underwater acoustic metamaterials via quasi-Helmholtz resonance: From low-frequency to ultra-broadband
Authors: Duan Mingyu , Yu Chenlei , Xin Fengxian , Lu Tian Jian
Published: February 2021

We report a lightweight tunable acoustic metamaterial with deep subwavelength thickness (e.g., λ/300) and strong load-bearing capability for underwater low-frequency and ultra-broadband acoustic perfect absorption. The metamaterial is constructed by introducing a rubber coating and an embedded metallic neck into a metallic hexagonal honeycomb Helmholtz resonator. Physically, the quasi-Helmholtz resonance triggered by the rubber coating together with the anti-phase cancellation caused by the embedded neck leads to superior sound absorption. Theoretical predictions of the metamaterial performance agree well with finite element simulation results. With fixed external morphology (e.g., honeycomb-cored sandwich panel) and fixed overall thickness (e.g., 50 mm), key internal geometrical parameters of the proposed metamaterial can be tailored to achieve tunable perfect absorption from, e.g., 100 Hz to 300 Hz. Further, combining such tunable quasi-Helmholtz resonance leads to ultra-broadband quasi-perfect absorption from, e.g., 306 Hz to 921 Hz. This work contributes to designing underwater acoustic metamaterials and controlling underwater acoustic waves.
Rogue waves for the fourth-order nonlinear Schrödinger equation on the periodic background
Authors: Zhang Hai-Qiang , Chen Fa
Published: February 2021

In this paper, we construct rogue wave solutions on the periodic background for the fourth-order nonlinear Schrödinger (NLS) equation. First, we consider two types of the Jacobi elliptic function solutions, i.e., dn- and cn-function solutions. Both dn- and cn-periodic waves are modulationally unstable with respect to the long-wave perturbations. Second, on the background of both periodic waves, we derive rogue wave solutions by combining the method of nonlinearization of spectral problem with the Darboux transformation method. Furthermore, by the study of the dynamics of rogue waves, we find that they have the analogs in the standard NLS equation, and the higher-order effects do not have effect on the magnification factor of rogue waves. In addition, when the elliptic modulus approaches 1, rogue wave solutions can reduce to multi-pole soliton solutions in which the interacting solitons form weakly bound states.
Coarse-grained simulation of PEGylated and tethered protein devices at all experimentally accessible surface residues on β-lactamase for stability analysis and comparison
Authors: Smith Addison K. , Soltani Mehran , Wilkerson Joshua W. , Timmerman Brandon D. , Zhao Emily Long , Bundy Bradley C. , Knotts Thomas A.
Published: February 2021

PEGylated and surface-tethered proteins are used in a variety of biotechnological applications, but traditional methods offer little control over the placement of the functionalization sites on the protein. Fortunately, recent experimental methods functionalize the protein at any location on the amino acid sequence, so the question becomes one of selecting the site that will result in the best protein function. This work shows how molecular simulation can be used to screen potential attachment sites for surface tethering or PEGylation. Previous simulation work has shown promise in this regard for a model protein, but these studies are limited to screening only a few of the surface-accessible sites or only considered surface tethering or PEGylation separately rather than their combined effects. This work is done to overcome these limitations by screening all surface-accessible functionalization sites on a protein of industrial and therapeutic importance (TEM-1) and to evaluate the effects of tethering and PEGylation simultaneously in an effort to create a more accurate screen. The results show that functionalization site effectiveness appears to be a function of super-secondary and tertiary structures rather than the primary structure, as is often currently assumed. Moreover, sites in the middle of secondary structure elements, and not only those in loops regions, are shown to be good options for functionalization—a fact not appreciated in current practice. Taken as a whole, the results show how rigorous molecular simulation can be done to identify candidate amino acids for functionalization on a protein to facilitate the rational design of protein devices.
Backward waves in the nonlinear regime of the Buneman instability
Authors: Tavassoli Arash , Shoucri Magdi , Smolyakov Andrei , Papahn Zadeh Mina , Spiteri Raymond J.
Published: February 2021

Observation of low- and high-frequency backward waves in the nonlinear regime of the Buneman instability is reported. Intense low-frequency backward waves propagating in the direction opposite to the electron drift (with respect to the ion population) of ions and electrons are found. The excitation of these waves is explained based on the linear theory for the stability of the electron velocity distribution function that is modified by nonlinear effects. In the nonlinear regime, the electron distribution exhibits a wide plateau formed by electron hole trapping and extends into the negative velocity region. It is shown that within the linear approach, the backward waves correspond to the weakly unstable or marginally stable modes generated by the large population of particles with negative velocities.
Texture evolution in nanocrystalline Ta under shock compression
Authors: Hu S. C. , Huang J. W. , Feng Z. D. , Zhang Y. Y. , Zhong Z. Y. , Cai Y. , Luo S. N.
Published: February 2021

We present systematic investigation on texture evolution in nanocrystalline Ta under planar shock wave loading at different impact velocities. Seven representative initial textures and two loading directions are studied via large-scale molecular dynamics simulations. Orientation mapping and texture analysis, including orientation distribution functions, pole figures, and inverse pole figures, are performed. Shock compression induces a ⟨221⟩ texture in nanocrystalline Ta initially with no texture, ⟨100⟩ fiber texture, {100}⟨100⟩ texture, and θ+γ rolling texture via twinning, which can be traced back to grains initially with ⟨100⟩. A ⟨100⟩ texture is induced via twinning for nanocrystalline Ta initially with no texture, ⟨110⟩ fiber texture, and α+γ rolling texture and can be traced back to ⟨110⟩. Dislocation slip and grain boundary sliding lead to the movement of ⟨110⟩ toward ⟨111⟩, and the strengthening of ⟨100⟩ and ⟨111⟩ orientation densities. The generation of new textures is observed for most cases. However, no new texture is found in the ⟨111⟩ fiber texture case for shock loading parallel to the fiber, and a much slower elastic–plastic transition occurs due to the lack of deformation twinning.
Direct comparison of wire, foil, and hybrid X-pinches on a 200 kA, 150 ns current driver
Authors: Collins G. W. , Valdivia M. P. , Hansen S. B. , Conti F. , Carlson L. C. , Hammer D. A. , Elshafiey A. , Narkis J. , Beg F. N.
Published: February 2021

Wire X-pinches (WXPs) have been studied comprehensively as fast (∼1 ns pulse width), small (∼1 μm) x-ray sources, created by twisting two or more fine wires into an “X” to produce a localized region of extreme magnetic pressure at the cross-point. Recently, two alternatives to the traditional WXP have arisen: the hybrid X-pinch (HXP), composed of two conical electrodes bridged by a thin wire or capillary, and the laser-cut foil X-pinch (LCXP), cut from a thin foil using a laser. We present a comparison of copper wire, hybrid, and laser-cut foil X-pinches on a single experimental platform: UC San Diego’s ∼200 kA, 150 ns rise time GenASIS driver. All configurations produced 1–2 ns pulse width, ≤5 μm soft x-ray (Cu L-shell, ∼1 keV) sources (resolutions diagnostically limited) with comparable fluxes. WXP results varied with linear mass and wire count, but consistently showed separate pinch and electron-beam-driven sources. LCXPs produced the brightest (∼1 MW), smallest (≤5 μm) Cu K-shell sources, and spectroscopic data showed both H-like Cu Kα lines indicative of source temperatures ≥2 keV, and cold Kα (∼8050 eV) characteristic of electron beam generated sources, which were not separately resolved on other diagnostics (within 1–2 ns and ≤200 μm). HXPs produced minimal K-shell emission and reliably single, bright, and small L-shell sources after modifications to shape the early current pulse through them. Benefits and drawbacks for each configuration are discussed to provide potential X-pinch users with the information required to choose the configuration best suited to their needs.
Two-step excitation induced photovoltaic properties in an InAs quantum dot-in-well intermediate-band solar cell
Authors: Zhu Yaxing , Asahi Shigeo , Watanabe Kohei , Miyashita Naoya , Okada Yoshitaka , Kita Takashi
Published: February 2021

Owing to the additional usage of sub-bandgap photons, the intermediate-band solar cell has been regarded as a promising device design to exceed the conversion limits of conventional photovoltaic devices. An output-voltage preservation is theoretically possible in this kind of device in the case of independent quasi-Fermi levels. This phenomenon manifests experimentally in a voltage recovery induced by supplementary two-step photon absorption processes. Here, we study the excitation-power and temperature dependences of the voltage performance in an intermediate-band solar cell containing InAs quantum dots in Al0.3Ga0.7As/GaAs quantum wells. The two-color photoexcitation method is used to separately control the interband and quantum dot-conduction band transitions. The output voltage is sensitive to the balance between the two excitation densities and the cell temperature. It is found that a strongly asymmetric irradiation can even lead to a voltage decrease. The temperature-dependent data suggest a faster electron–hole annihilation at lower temperatures. We introduce a new characteristic index to qualitatively evaluate the carrier loss in the intermediate band.
Room temperature rectification in tapered-channel thermal diodes through nanoscale confinement-induced liquid–solid phase change
Authors: Jacobs Matt , Zhou Xinran , Olivera Edgar , Sheil Ryan , Huang Shu , Marszewski Michal , Chang Jane , Tolbert Sarah , Osher Stanley , Pilon Laurent , Marian Jaime
Published: February 2021

Designing thermal diodes is attracting a considerable amount of interest recently due to the wide range of applications and potentially high impact in the transportation and energy industries. Advances in nanoscale synthesis and characterization are opening new avenues for design using atomic-level tools to take advantage of materials properties in confined volumes. In this paper, we demonstrate using advanced modeling and simulation the rectification properties of tapered-channel thermal diodes relying on asymmetric heat flow brought about by thermal conductivity differences between the liquid and solid phases of suitably selected phase-change materials (PCM). Our prototypical design considers Ga as PCM and anodized alumina as the structural material. First, we use a thresholding scheme to solve a Stefan problem in the device channel to study the interface shape and the hysteresis of the phase transformation when the temperature gradient is switched. We then carry out finite-element simulations to study the effect of several geometric parameters on diode efficiency, such as channel length as aspect ratio. Our analysis establishes physical limits on rectification efficiencies and point to design improvements using several materials to assess the potential of these devices as viable thermal diodes. Finally, we demonstrate the viability of proof-of-concept device fabrication by using a non-conformal atomic layer deposition process in anodic alumina membranes infiltrated with Ga metal.
Impact of electron temperature anisotropy on the collisionless tearing mode instability in the presence of a strong guide field
Authors: Granier C. , Tassi E. , Borgogno D. , Grasso D.
Published: February 2021

We derive and analyze a dispersion relation for the growth rate of collisionless tearing modes, driven by electron inertia and accounting for equilibrium electron temperature anisotropy in a strong guide field regime. For this purpose, a new gyrofluid model is derived and subsequently simplified to make the derivation of the dispersion relation treatable analytically. The main simplifying assumptions consist in assuming cold ions, neglecting electron finite Larmor radius effects, decoupling ion gyrocenter fluctuations, and considering β⊥e≪1, with β⊥e indicating the ratio between the perpendicular electron thermal pressure and the magnetic pressure exerted by the guide field. This simplified version of the gyrofluid model is shown to possess a noncanonical Hamiltonian structure. The dispersion relation is obtained by applying the theory of asymptotic matching and does not predict an enhancement of the growth rate as the ratio Θe between perpendicular and parallel equilibrium electron temperatures increases. This indicates a significant difference with respect to the case of absent or moderate guide field. For an equilibrium magnetic shear length of the order of the perpendicular sonic Larmor radius and at a fixed β⊥e, we obtain that the tearing mode in the strong guide field regime gets actually weakly damped, as Θe increases. In the isotropic limit Θe=1, the dispersion relation reduces to a previously known formula. The analytical predictions are tested against numerical simulations, showing a very good quantitative agreement. We also provide a detailed discussion of the range of validity of the derived dispersion relation and of the compatibility among the different adopted assumptions.
Polymer brushes with reversibly tunable grafting density
Authors: Klushin Leonid I. , Skvortsov Alexander M. , Polotsky Alexey A. , Ivanova Anna S. , Schmid Friederike
Published: February 2021

We propose a novel class of responsive polymer brushes, where the effective grafting density can be controlled by external stimuli. This is achieved by using end-grafted polymer chains that have an affinity to the substrate. For sufficiently strong surface interactions, a fraction of chains condenses into a near-surface layer, while the remaining ones form the outer brush. The dense layer and the more tenuous outer brush can be seen as coexisting microphases. The effective grafting density of the outer brush is controlled by the adsorption strength and can be changed reversibly and in a controlled way as a response to changes in environmental parameters. The effect is demonstrated by numerical self-consistent field calculations and analyzed by scaling arguments. Since the thickness of the denser layer is about a few monomer sizes, its capacity to form a microphase is limited by the product of the brush chain length and the grafting density. We explore the range of chain lengths and grafting densities where the effect is most pronounced. In this range, the SCF studies suggest that individual chains inside the brush show large rapid fluctuations between two states that are separated by only a small free energy barrier. The behavior of the brush as a whole, however, does not reflect these large fluctuations, and the effective grafting density varies smoothly as a function of the control parameters.
Performance of decoupled electroaerodynamic thrusters
Authors: Gomez-Vega Nicolas , Xu Haofeng , Abel James M. , Barrett Steven R. H.
Published: February 2021

Solid-state aerodynamic devices, which use electroaerodynamics (EAD) to produce a propulsive force, have the potential to make drones and airplanes significantly quieter and may provide benefits in sustainability and manufacturability. In these devices, ions are accelerated between two electrodes by an electric field, colliding with neutral air molecules and producing an ionic wind and a thrust force. The authors' previous work showed that a “decoupled” device architecture, which separates the ionization and ion acceleration processes, can increase thrust density and thrust-to-power compared to the prevailing corona-discharge-based EAD architecture, which uses a single DC potential for both processes. However, the discharge characteristics of this decoupled architecture have not been previously determined. Here, we experimentally characterize a decoupled EAD thruster with a wire-to-wire dielectric barrier discharge (DBD) ion source: an AC voltage drives the DBD, which ionizes neutral air molecules at the emitting electrode, while a separate DC voltage accelerates ions toward the collecting electrode. We determine the discharge characteristics (i.e., the DC-current-to-DC-voltage relationship) of this decoupled thruster as well as a model for the interaction between the ionization and acceleration stages: we find that the former takes the same functional form as the analytical solution for space-charge limited current in a thin collisional ion channel, whereas the latter is determined primarily by the power draw of the DBD ionization stage. We present a complete model for the thrust and power draw of decoupled EAD thrusters, enabling their quantitative design and optimization for use in aircraft propulsion and other applications.
Strain-controlled electrical and magnetic properties of SrRuO3 thin films with Sr3Al2O6 buffer layers
Authors: Hu Chuan-Zhu , Zhang You-Shan , Niu Xu , Zhong Ni , Xiang Ping-Hua , Duan Chun-Gang
Published: February 2021

SrRuO3 (SRO) thin films have been grown on a (001)-oriented SrTiO3 substrate with Sr3Al2O6 (SAO) buffer layers using pulsed laser deposition. X-ray diffraction results reveal that the epitaxial strain of SRO changes from compressive to relaxed or tensile ones by tuning the thickness of the SAO buffer layer (tSAO). We have demonstrated that the variation of strain has a strong influence on the microstructure and electrical and magnetic properties of SRO. When tSAO < 10 nm, the epitaxial strain is relaxed and the SRO film possesses higher Curie temperature resembling that of SRO bulk. Upon further increasing tSAO ≥ 10 nm, the SRO films are subjected to tensile strain, showing a typical step-and-terrace surface and coherent epitaxy characteristic on the SAO buffer layer. The electrical and magnetic properties of SRO are very sensitive to buffer layer-controlled epitaxial strain. The tensile strained SRO films show quite different electrical transport properties at low temperature, i.e., appearance of metal-insulator transition and positive magnetoresistances and the absence of non-Fermi-liquid behavior. Additionally, magnetic anisotropy is found in both the tensile and the compressively strained SRO, while the strain-relaxed film shows isotropic magnetization. Based on the electrical and magnetic properties, a phase diagram of SRO on the SAO buffer layer has been constructed.
Too big, too small, or just right? A benchmark assessment of density functional theory for predicting the spatial extent of the electron density of small chemical systems
Authors: Hait Diptarka , Liang Yu Hsuan , Head-Gordon Martin
Published: February 2021

Multipole moments are the first-order responses of the energy to spatial derivatives of the electric field strength. The quality of density functional theory prediction of molecular multipole moments thus characterizes errors in modeling the electron density itself, as well as the performance in describing molecules interacting with external electric fields. However, only the lowest non-zero moment is translationally invariant, making the higher-order moments origin-dependent. Therefore, instead of using the 3 × 3 quadrupole moment matrix, we utilize the translationally invariant 3 × 3 matrix of second cumulants (or spatial variances) of the electron density as the quantity of interest (denoted by K). The principal components of K are the square of the spatial extent of the electron density along each axis. A benchmark dataset of the principal components of K for 100 small molecules at the coupled cluster singles and doubles with perturbative triples at the complete basis set limit is developed, resulting in 213 independent K components. The performance of 47 popular and recent density functionals is assessed against this Var213 dataset. Several functionals, especially double hybrids, and also SCAN and SCAN0 predict reliable second cumulants, although some modern, empirically parameterized functionals yield more disappointing performance. The H, Li, and Be atoms, in particular, are challenging for nearly all methods, indicating that future functional development could benefit from the inclusion of their density information in training or testing protocols.
Wall friction should be decoupled from fluid viscosity for the prediction of nanoscale flow
Authors: Zhou Runfeng , Sun Chengzhen , Bai Bofeng
Published: February 2021

The accurate determination of fluid viscosity based on the microscopic information of molecules is very crucial for the prediction of nanoscale flow. Despite the challenge of this problem, researchers have done a lot of meaningful work and developed several distinctive methods. However, one of the common approaches to calculate the fluid viscosity is using the Green–Kubo formula by considering all the fluid molecules in nanospace, inevitably causing the involvement of the frictional interaction between fluid and the wall into the fluid viscosity. This practice is certainly not appropriate because viscosity is essentially related only to the interactions among fluid molecules. Here, we clarify that the wall friction should be decoupled from fluid viscosity by distinguishing the frictional region and the viscous region for the accurate prediction of nanoscale flow. By comparing the fluid viscosities calculated from the Green–Kubo formula in the whole region and viscous region and the viscosity obtained from the velocity profile through the Hagen–Poiseuille equation, it is found that only the calculated viscosity in the viscous region agrees well with the viscosity from the velocity profile. To demonstrate the applicability of this clarification, the Lennard-Jones fluid and water confined between Lennard-Jones, graphene, and silica walls, even with different fluid–wall interactions, are extensively tested. This work clearly defines the viscosity of fluids at nanoscales from the inherent nature of physics, aiming at the accurate prediction of nanoscale flow from the classical continuum hydrodynamic theory.
On interrelations between trivial and nontrivial basic sets of structurally stable diffeomorphisms of surfaces
Authors: Grines Vyacheslav , Mints Dmitrii
Published: February 2021

The article is devoted to interrelations between an existence of trivial and nontrivial basic sets of A-diffeomorphisms of surfaces. We prove that if all trivial basic sets of a structurally stable diffeomorphism of surface M2 are source periodic points α1,…αk, then the non-wandering set of this diffeomorphism consists of points α1,…,αk and exactly one one-dimensional attractor Λ. We give some sufficient conditions for attractor Λ to be widely situated. Also, we prove that if a non-wandering set of a structurally stable diffeomorphism contains a nontrivial zero-dimensional basic set, then it also contains source and sink periodic points.
Equation-of-state, sound speed, and reshock of shock-compressed fluid carbon dioxide
Authors: Crandall L. E. , Rygg J. R. , Spaulding D. K. , Huff M. F. , Marshall M. C. , Polsin D. N. , Jeanloz R. , Boehly T. R. , Zaghoo M. , Henderson B. J. , Brygoo S. , Celliers P. M. , Eggert J. H. , Fratanduono D. E. , Lazicki A. , Millot M. , Collins G. W.
Published: February 2021

Mechanical equation-of-state data of initially liquid and solid CO2 shock-compressed to terapascal conditions are reported. Diamond-sapphire anvil cells were used to vary the initial density and state of CO2 samples that were then further compressed with laser-driven shock waves, resulting in a data set from which precise derivative quantities, including Grüneisen parameter and sound speed, are determined. Reshock states are measured to 800 GPa and map the same pressure-density conditions as the single shock using different thermodynamic paths. The compressibility data reported here do not support current density-functional-theory calculations, but are better represented by tabular equation-of-state models.
Liquid–liquid phase transition in molten cerium during shock release
Authors: Xu Liang , Wang Zhigang , Li Zhiguo , Li Xuhai , Yao Songlin , Li Jun , Zhou Xianming , Yu Yuying , Hu Jianbo , Wu Qiang
Published: February 2021

The identification of the liquid–liquid phase transition (LLPT) in liquids under shock compression is a long-standing challenge. In this Letter, by designing shock-release experiments in shock-driven molten Ce, we observe a first-order LLPT along the release path. The volume change associated with the transition is less than 6%, much smaller than the one (14%) obtained in static compression experiments, indicating that the LLPT in molten Ce is strongly rate dependent. The identified timescale for the LLPT is on the order of 200 ns. Our results, therefore, provide kinetic information of the LLPT in an unprecedented manner, which is extremely valuable for the construction of a non-equilibrium phase diagram.
Research on fault detection of asymmetric piecewise well-posed stochastic resonance system
Authors: Zhang Gang , Liu Yilin , He Lifang
Published: February 2021

Stochastic resonance of an asymmetric piecewise well-posed system driven by a periodic forcing and Gaussian white noise is investigated. Aiming at the problem that the output saturation of the classical stochastic resonance (CSR) system needs to be further improved, the dimensionality of the quartic function is reduced to a quadratic function, and the well position of the function becomes asymmetric. First, the potential function and mean first passage time are analyzed, and then the signal to noise ratio formula of the system is derived through adiabatic approximation theory. Second, the system is simulated and tested. Theoretical analysis and numerical simulation show that the system in a well-posed symmetric case has better performance than the CSR system, but is better in a well-posed asymmetric case. Finally, the bearing fault detection is processed by using the proposed system. The results show that the fault frequency can be more accurately identified by the well-posed asymmetry, and the energy of the characteristic signal can be improved further. The theoretical basis and reference value of the system are provided for further application in practical engineering testing.
Invisibility cloaking with passive and active Huygens's metasurfaces
Authors: Ang Paris , Xu Gengyu , Eleftheriades George V.
Published: February 2021

According to the Equivalence Principle, any distribution of electromagnetic fields can be generated within a closed region by suitable electric and magnetic sources lying on its bounding surface. In electromagnetic theory, these sources have been used as fictitious analytical tools. However, this has changed in recent years with the development of “Huygens's metasurfaces,” which are subwavelength thin sheets of artificial active and/or passive elements. With proper configuration, these elements can physically approximate the aforementioned sources, enabling precise manipulation of electromagnetic waves in extraordinary manners. Given their potential, this work aims to provide an overview of Huygens's metasurfaces with a focus on cloaking applications. After an exposition of general operation and design principles, both active and passive Huygens's cloaks are described.
Nonselective cation permeation in an AMPA-type glutamate receptor
Authors: Biedermann Johann , Braunbeck Sebastian , Plested Andrew J. R. , Sun Han
Published: February 2021

Significance

AMPA-type glutamate receptors (AMPARs) make the final step in a relay of excitability from one brain cell to another. The receptor contains an integral ion channel, which, when opened by neurotransmitter, permits sodium and other cations to cross the cell membrane. We investigated permeation of sodium, potassium, and cesium at the atomistic level using a computational molecular dynamics approach and obtained ion transit rates similar to those in wet experiments over tens of microseconds of simulations. We determined that the region selecting between cations is the simplest of any channel of this type. Distinct from ion channels that select single ion species, sodium and potassium remain partly hydrated and have only one major binding site in the channel.
Ferromagnetic liquid droplets with adjustable magnetic properties
Authors: Wu Xuefei , Streubel Robert , Liu Xubo , Kim Paul Y. , Chai Yu , Hu Qin , Wang Dong , Fischer Peter , Russell Thomas P.
Published: February 2021

Significance

Structured functional liquids combine mechanical versatility of fluids with solid-state properties, such as ferromagnetism, and offer a route to synthesize and control magnetic liquids for adaptive liquid robotics. Studies on these intriguing materials are only in their nascent state, and a profound understanding of the physical state is still lacking. We use hydrodynamics experiments to probe how the magnetization of ferromagnetic liquid droplets, governed by the assembly and jamming of magnetic nanoparticles at liquid–liquid interfaces, and their response to external stimuli can be tuned by chemical, structural, and magnetic means. Our results highlight the leading role of structural short-range order on magnetic properties, which provide a path toward nano-patterning structured liquids.
The Reluctant Warrior: Semiotic Notes on the Story of Zāl in theShāhnāmeh
Authors: Omidsalar Mahmoud , Afshinvafaie Mohammad
Published: February 2021

Zāl is the embodiment of the heroic culture which shapes and determines the conduct of the Shāhnāmeh heroes from Manūchihr through Rustam's death. For Zāl to attain that level of moral authority, the poem semiotically endows him with innate wisdom symbolized by his white hair at birth. By the end of the story, when he is still a relatively young man, he has gained the authority to change the ruling dynasty by choosing and crowning kings at will (e.g. his crowning of Zav and Kayqubād). Zāl's story is thus a tale of transformation thatseamlesslyfits into the overall narrative of theShāhnāmeh.It helps the poem's narrativemake the transition from the age of ancient kings in whom heroism, royal authority, and magical potency are combined, to the era of a different line of rulers who govern by royal authority alone. This process moves in two parallel lines: the transfer of the magical wisdom of the primordial kings to the person of a sage who functions as the embodiment of sagacity and prudence, and the transfer of their heroic aspect to a great warrior who serves as the country's “chief hero,” its jahān pahlawān. With the exception of Kaykhosraw, whose character has very strong supernatural and religious dimensions, every important legendary king after Manūchihr has a sage on whose advice he depends (e.g. Zav, Kayqubād and Kaykāvūs have Zāl, Gushtāsp has Jāmāsp, and Alexander has Aristotle). The king also has a warrior who holds the office of the jahān pahlawān (Kaykāvūs and Kaykhusraw have Rustam, Luhrāsp has Zarēr, and Gushtāsp has Isfandiyār).
Linguistic indicators of text quality in analytical texts: developmental changes and sensitivity to pedagogical work (Indicadores lingüísticos de la calidad textual en los textos analíticos: cambios evolutivos y sensibilidad al trabajo pedagógico)
Authors: Aparici Melina , Cuberos Rocío , Salas Naymé , Rosado Elisa
Published: February 2021

Mastering analytical writing involves the proficient use of varied later-acquired grammatical, lexical and discourse forms and functions. Developmental studies have identified specific linguistic features as diagnostic of increasing proficiency. This study examines how these features change throughout educational levels and before and after the implementation of a set of classroom activities aimed at homogenizing participants’ pedagogical input while raising their awareness of analytical texts’ main functions. Two hundred and twelve Spanish speakers from primary, secondary and university levels participate in the study, each producing two analytical texts. The corpus consists of 424 texts produced on the same topic. Results indicate that not all the features pertaining to the same domain show identical changes across educational levels or are identically sensitive to pedagogical work. Productivity measures increase with educational level and after pedagogical work, except for university students. Most lexical, syntactic and discourse-level measures improve with educational level, though their sensitivity to pedagogical work is not straightforward. Findings suggest the need to evaluate writing quality at a high level of granularity.
The gender of dependency theory: women as workers, from neocolonialism in West Africa to the implosion of contemporary capitalism
Authors: Scott Catherine
Published: February 2021

Samir Amin’s large body of work affords an opportunity to trace the ways in which he analysed class and gender in the workings of neocolonialism in the aftermath of independence in West Africa and globalisation after the end of the Cold War. Using two key texts, Neo-colonialism in West Africa (1973) and The implosion of contemporary capitalism (2013), this paper traces the way women, gender and dependency theory in Amin’s theoretical framework operate to simultaneously suggest and then foreclose recognition of how gender analysis provides vital, independent perspectives on global inequality.
The effect of custom‐fitted compression garments worn overnight for recovery from judo training in elite athletes
Authors: Brown Freddy C.W. , Hill Jessica A. , van Someren Ken , Howatson Glyn , Pedlar Charles R.
Published: February 2021

This study investigated the effects of custom‐fitted compression garments (CG) worn during recovery over a multi‐day training camp in elite judo players (judoka). A single blind, placebo‐controlled study was carried out in 11 elite judoka, using a two‐way crossover design. Two three‐day training camps were completed in CG and placebo conditions in a random order. Changes in performance and physiological markers were compared between conditions. Judoka were assessed before training for (maximal) isometric knee extension and grip strength, countermovement jump performance and bench‐press velocity, alongside soreness, limb circumferences, plasma creatine kinase activity (CK) and perceived bruising. Measurements were repeated after 12, 36 and 43 h of training, whereupon judoka rated the effectiveness of each intervention. Knee extension and bench‐press performance demonstrated significant familiarization (p < 0.001), and were excluded from subsequent analysis. Jump performance was unaffected by training (p > 0.05). Grip strength declined throughout training (p < 0.001), with peak decrements of −9.7% indicating mild muscle damage. Increases in bruising, CK and soreness demonstrated highly variable, if significant (p < 0.001) responses. Although CG were perceived as significantly more effective than placebo for recovery (p = 0.046), no effects were observed for any other outcome (p > 0.05). Compression conferred no statistically significant impact upon recovery markers in elite judoka throughout training. Muscle damage responses were inconsistent in this population. Individual athletes would be advised to monitor habitually‐used performance measures while using CG to ascertain whether perceptual benefits translate into enhanced recovery.

Highlights

Compression garments were perceived as more effective for recovery than placebo by elite judoka.

However, no measures of performance or muscle damage were enhanced by CG.

Randori was associated with inconsistent muscle damage responses in elite judoka, while lower‐body performance was not impaired.

Individual athletes would be advised to monitor habitually‐used performance measures while using CG to ascertain whether perceptual benefits translate into enhanced recovery.
On the quasi-position representation in theories with a minimal length
Authors: Bosso Pasquale
Published: February 2021

Quantum mechanical models with a minimal length are often described by modifying the commutation relation between position and momentum. Although this represents a small complication when described in momentum space, at least formally, the (quasi-)position representation acquires numerous issues, source of misunderstandings. In this work, we review these issues, clarifying some of the aspects of minimal length models, with particular reference to the representation of the position operator.
The pedagogical representation of mass functions with LEGO and their origin
Authors: Kautsch Stefan J , Veras Dimitri , Hansotia Kyle K
Published: February 2021

We promote the teaching of mass functions as an integral part of an interdisciplinary science education. Mass functions characterize the frequency distributions of objects with different masses on all cosmic scales. We intend to enhance experiential learning of this concept with a creative LEGO brick experiment for a diverse student audience. To our surprise, the LEGO mass function is not only qualitatively but also quantitatively comparable to mass functions found across the Universe. We also discuss the relation between gravitation and mass distributions as a possible explanation for the continuity of the universal mass function.
Sacrificial grid release technology: a versatile release concept for MEMS structures
Authors: Zhao Y , Janssens Y L , Veltkamp H-W , de Boer M J , Groenesteijn J , Tas N R , Wiegerink R J , Lötters J C
Published: February 2021

Micro-electro-mechanical-systems (MEMS) structures with different in-plane dimensions often need to be released simultaneously from the bulk of the wafer and a single dry etching or wet etching technique cannot fulfill all release requirements. In this paper we present a universally applicable solution to release MEMS structures with different surface areas in a controlled and uniform way, which combines isotropic etching of a sacrificial silicon support structure by xenon difluoride with a predefined etch surface made by deep reactive ion etching. Two applications of this Sacrificial Grid Release Technology are presented, in which MEMS devices are released in silicon-on-insulator wafers. The demonstrated applications involve the release of microstructures with in-plane dimensions ranging from tens of micrometers to a few millimeters. The sacrificial silicon structure provides mechanical support which allows freedom in process flow design for fragile MEMS structures. The release technique can also be used to separate the chips from the wafer.
Experimental investigation of ignition by multichannel gliding arcs in a swirl combustor
Authors: Lin Dong , Jia Min , Zhang Zhibo , Song Huimin , Cui Wei , Wang Weizhen , Cai Banghuang
Published: February 2021

In the extreme conditions of high altitude, low temperature, low pressure and high speed, the aircraft engine has a strong tendency to extinguish and it is then difficult to start secondary ignition, which means that re-ignition of the aircraft engine faces great challenges. Additionally, the ability of the single-channel gliding arc (1-GA) in assisting the ignition under extreme conditions is weak. In this paper, to solve this problem, a multichannel gliding arcs (MGA) system is proposed, using the principle of multichannel discharge. Experiments on the electrical characteristics and ignition performance of MGA were conducted under atmospheric pressure in a swirl model combustor. The electrical characteristics of MGA were investigated under different air velocities. The ignition process of MGA was recorded by using a high-speed camera with CH* filter. Results show that the three-channel gliding arcs (3-GA) and five-channel gliding arcs (5-GA) generated more averaged power than the 1-GA under a constant air velocity. For example, the 3-GA and 5-GA generated 112.8% and 187.3% more averaged power than that of the 1-GA at 74.6 m s−1, respectively. The arc shapes of gliding arcs with different channel numbers were different and the duration time of ‘breakdown-stretching-extinguishing’ of MGA shortened. Furthermore, compared with the 1-GA, the percentage of the lean ignition limit widening of the 3-GA and 5-GA can reach 13.5% and 20.9% respectively. The frequency of re-breakdown in the discharge process using different gliding arc channel numbers is different, which can continuously inject energy into the combustor and generate the ‘flame combination’ phenomenon producing a larger flame area. The ignition process of MGA can be divided into three stages: sliding stage, flame combination stage and flame stabilization stage.
VSe2 quantum dots with high-density active edges for flexible efficient hydrogen evolution reaction
Authors: Wang Chaolun , Jin Mengge , Liu Dongming , Liang Fang , Luo Chen , Li Panlin , Cai Chunhua , Bi Hengchang , Wu Xing , Di Zengfeng
Published: February 2021

Two-dimensional (2D) metallic transition metal dichalcogenides (TMDCs) with large specific surface areas and high conductivities are promising catalysts for electrocatalytic hydrogen production. The highly active edges of the 2D metallic TMDCs are the desirable catalytic sites for the hydrogen evolution reaction (HER). Herein, the vanadium diselenide (VSe2) quantum dots with high-density edge sites are prepared by tip sonication of the self-detached VSe2 nanosheets. The spontaneously released VSe2 nanosheets, without chemical-involved transfer, offer a noncontaminated catalyst for HER. Compared to the VSe2 nanosheets, VSe2 quantum dots with a high density of active edges present a significant enhancement of the electrocatalytic performance. The reduced overpotential and transfer resistance indicate the lower Gibbs free energy and faster faradic process of the VSe2 quantum dots for HER. The active edge sites of VSe2 quantum dots show improved catalytic properties in thermodynamic and kinetic aspects. The VSe2 quantum dots loaded on a carbon cloth could be used as a flexible electrode for HER. This work provides an effective way to regulate the defects of the 2D TMDCs for high-performance HER catalysts and also offers a catalyst for flexible HER.
Charge. transport, conductivity and Seebeck coefficient in pristine and TCNQ loaded preferentially grown metal-organic framework films
Authors: Chen Xin , Zhang Kai , Hassan Zeinab Mohamed , Redel Engelbert , Baumgart Helmut
Published: February 2021

This investigation on metal-organic framework (MOF) HUKUST-1 films focuses on comparing the undoped pristine state and with the case of doping by TCNQ infiltration of the MOF pore structure. We have determined the temperature dependent charge transport and p-type conductivity for HKUST-1 films. Furthermore, the electrical conductivity and the current–voltage characteristics have been characterized in detail. Because the most common forms of MOFs, bulk MOF powders, do not lend themselves easily to electrical characterization investigations, here in this study the electrical measurements were performed on dense, compact surface-anchored metal-organic framework (SURMOF) films. These monolithic, well-defined, and (001) preferentially oriented MOF thin films are grown using quasi-liquid phase epitaxy (LPE) on specially functionalized silicon or borosilicate glass substrates. In addition to the pristine SURMOF films also the effect of loading these porous thin films with TCNQ has been investigated. Positive charge carrier conduction and a strong anisotropy in electrical conduction was observed for highly oriented SURMOF films and corroborated with Seebeck coefficient measurements. Van der Pauw four-point Hall sample measurements provide important insight into the electrical behavior of such porous and hybrid organic–inorganic crystalline materials, which renders them attractive for potential use in microelectronic and optoelectronic devices and thermoelectric applications.
General theory of electroadhesion
Authors: Persson Bo N J
Published: February 2021

We present a general theory of electroadhesion assuming layered materials with finite electric conductivity and an air gap resulting from interfacial surface roughness. The theory reduces to the results derived in Persson (2018 J. Chem. Phys.
148 144701) in the appropriate limits. We present numerical results to illustrate the theory.
Detection of impact on aircraft composite structure using machine learning techniques
Authors: Ai Li , Soltangharaei Vafa , Bayat Mahmoud , Van Tooren Michel , Ziehl Paul
Published: February 2021

Aircraft structures are exposed to impact damage caused by debris and hail during their service life. One of the design concerns in composite structures is the resistance of layered surfaces to damage, which occurs from impacts with various foreign objects. Therefore, the impact localization and damage quantification of impacts should be studied and considered to address flight safety and to reduce costs associated with a regularly scheduled visual inspection. Since the structural components of the aircraft are large scale, visual inspection and monitoring are challenging and subject to human error. This paper presents a promising solution that can automatically detect and localize an impact that may occur during flight. To achieve this goal, acoustic emission (AE) is employed as an impact monitoring approach. Random forest and deep learning were adopted for training the source location models. An AE dataset was collected by conducting an impact experiment on a full-size thermoplastic aircraft elevator in a laboratory environment. A dataset consisting of AE parametric features and a dataset consisting of AE waveforms were assigned to a random forest classifier and deep learning network for the investigation of their applicability of impact source localization. The results obtained were compared using the source localization approach in previous research using a conventional artificial neural network. The analysis of results shows the random forest and deep learning leads to better event localization performance. In addition, the random forest model can provide the importance of features. By deleting the least important features, the storage required to save the input and the computing time for the random forest is greatly reduced, and an acceptable localization performance can still be obtained.
Nanoindentation of mesenchymal stem cells using atomic force microscopy: effect of adhesive cell-substrate structures
Authors: Migliorini Elisa , Cavalcanti-Adam Elisabetta Ada , Uva Antonio Emmanuele , Fiorentino Michele , Gattullo Michele , Manghisi Vito Modesto , Vaiani Lorenzo , Boccaccio Antonio
Published: February 2021

The procedure commonly adopted to characterize cell materials using atomic force microscopy neglects the stress state induced in the cell by the adhesion structures that anchor it to the substrate. In several studies, the cell is considered as made from a single material and no specific information is provided regarding the mechanical properties of subcellular components. Here we present an optimization algorithm to determine separately the material properties of subcellular components of mesenchymal stem cells subjected to nanoindentation measurements. We assess how these properties change if the adhesion structures at the cell-substrate interface are considered or not in the algorithm. In particular, among the adhesion structures, the focal adhesions and the stress fibers were simulated. We found that neglecting the adhesion structures leads to underestimate the cell mechanical properties thus making errors up to 15%. This result leads us to conclude that the action of adhesion structures should be taken into account in nanoindentation measurements especially for cells that include a large number of adhesions to the substrate.