bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of radial electric field on ion temperature gradient driven mode stability
Authors: Chen Ningfei , Hu Hanyuan , Zhang Xiangyu , Wei Shizhao , Qiu Zhiyong
Published: April 2021

The local stability of ion-temperature gradient driven mode (ITG) in the presence of a given radial electric field is investigated using gyrokinetic theory and ballooning mode formalism with toroidal effect accounted for. It is found that zero frequency radial electric field-induced poloidal rotation can significantly stabilize ITG, while the associated density perturbation has little effect on ITG stability due to the modification of finite-orbit-width effect. However, the parallel mode structure is slightly affected due to the evenly symmetric density modulation associated with the zero-frequency radial electric field.
Ultra-low-vibration closed-cycle cryogenic surface-electrode ion trap apparatus
Authors: Dubielzig T. , Halama S. , Hahn H. , Zarantonello G. , Niemann M. , Bautista-Salvador A. , Ospelkaus C.
Published: April 2021

We describe the design, commissioning, and operation of an ultra-low-vibration closed-cycle cryogenic ion trap apparatus. One hundred lines for low-frequency signals and eight microwave/radio frequency coaxial feed-lines offer the possibility of implementing a small-scale ion-trap quantum processor or simulator. With all supply cables attached, more than 1.3 W of cooling power at 5 K is still available for absorbing energy from electrical pulses introduced to control ions. The trap itself is isolated from vibrations induced by the cold head using a helium exchange gas interface. The performance of the vibration isolation system has been characterized using a Michelson interferometer, finding residual vibration amplitudes on the order of 10 nm rms. Trapping of 9Be+ ions has been demonstrated using a combination of laser ablation and photoionization.
Necessary criteria for Markovian divisibility of linear maps
Authors: Caro Matthias C. , Graswald Benedikt R.
Published: April 2021

We describe how to extend the notion of infinitesimal Markovian divisibility from quantum channels to general linear maps and compact and convex sets of generators. We give a general approach toward proving necessary criteria for (infinitesimal) Markovian divisibility. With it, we prove two necessary criteria for infinitesimal divisibility of quantum channels in any finite dimension d: an upper bound on the determinant in terms of a Θ(d)-power of the smallest singular value and in terms of a product of Θ(d) smallest singular values. These allow us to analytically construct, in any given dimension, a set of channels that contains provably non-infinitesimal Markovian divisible ones. Moreover, we show that, in general, no such non-trivial criteria can be derived for the classical counterpart of this scenario.
Study of resistive switching, photoresponse, and magnetism modulation in the Pt/Co3O4/Nb:SrTiO3 heterostructure
Authors: Zhao Meng , Zhu Yongdan , Zhang Yuan , Zhang Teng
Published: April 2021

Co3O4 thin films are epitaxially grown on an Nb-doped (001) SrTiO3 (NSTO) single-crystal substrate using pulsed laser deposition to form Pt/Co3O4/NSTO heterostructures. These devices display stable bipolar resistive switching (RS) with multilevel memory, good endurance, and a maximum ON/OFF ratio of up to 104. The high resistance state of the device exhibits significant photoresponse characteristics with an open-circuit voltage of 0.47 V, under the illumination of a 405 nm laser. Moreover, the saturation magnetization of the Co3O4 film shows reversible switching associated with different resistance states. The RS and related photoelectricity could be attributed to the modulation of the potential barrier via the oxygen vacancy migration coupled with electron trapping/detrapping and light illumination at the Co3O4/NSTO interface; meanwhile, the change in magnetism might be due to the redistribution of the oxygen vacancies. These results provide a promising pathway for developing multifunctional, multilevel memory devices with RS, photoresponse, and magnetism.
Remarks on periodic Jacobi matrices on trees
Authors: Christiansen Jacob S. , Simon Barry , Zinchenko Maxim
Published: April 2021

We look at periodic Jacobi matrices on trees. We provide upper and lower bounds on the gap of such operators analogous to the well-known gap in the spectrum of the Laplacian on the upper half-plane with a hyperbolic metric. We make some conjectures about antibound states and make an interesting observation for the so-called rg-model where the underlying graph has r red and g green vertices and where any two vertices of different colors are connected by a single edge.
Analysis of influences of pressure anisotropies on the 3D MHD equilibrium in LHD
Authors: Romba T. , Suzuki Y. , Proll J. H. E.
Published: April 2021

3D equilibria with an anisotropic pressure component in the large helical device are analyzed with respect to their magnetic axis locations. The anisotropic extension of the 3D equilibrium solver variational moments equilibrium code, anisotropic neumann inverse moments equilibrium code, is used to compute fixed-boundary plasma equilibria based on a bi-Maxwellian distribution function describing the anisotropic particles. Different heating scenarios are assessed by means of parallel and perpendicular pressure anisotropies with different radial anisotropic pressure profiles imposed. A theoretical predicted scaling of the magnetic axis location with the auxiliary parameter βeq as predicted for classical stellarators and heliotrons by Hitchon [Nucl. Fusion 23, 383 (1983)] is found to be applicable to the large helical device in the case of a flat hot-particle profile for parallel or weak perpendicular dominated anisotropies with β⊥/β∥≤2. For strong perpendicular or non-flat hot-particle profiles, a deviation from the predicted scaling of the magnetic axis location is found. Whereas center-peaked profiles show a stronger shift of the magnetic axis, edge-peaked profiles show no significant change of its radial location. High critical magnetic fields are identified as a necessary condition for strong perpendicular anisotropies. The observed deviations are ascribed to the magnetic field structure and negative pressure gradients. The invalidity of the theoretical predictions in the case of certain configurations is found to be caused by higher-order terms in the pressure components, which are not accounted for by the ordering on which the theory is based.
Finite-part integration in the presence of competing singularities: Transformation equations for the hypergeometric functions arising from finite-part integration
Authors: Villanueva Lloyd L. , Galapon Eric A.
Published: April 2021

Finite-part integration is a recently introduced method of evaluating convergent integrals by means of the finite-part of divergent integrals [E. A. Galapon, Proc. R. Soc., A 473, 20160567 (2017)]. Current application of the method involves exact and asymptotic evaluation of the generalized Stieltjes transform ∫0af(x)/(ω+x)ρdx under the assumption that the extension of f(x) in the complex plane is entire. In this paper, the method is elaborated further and extended to accommodate the presence of competing singularities of the complex extension of f(x). Finite-part integration is then applied to derive consequences of known Stieltjes integral representations of the Gauss function and the generalized hypergeometric function that involve Stieltjes transforms of functions with complex extensions having singularities in the complex plane. Transformation equations for the Gauss function are obtained from which known transformation equations are shown to follow. In addition, building on the results for the Gauss function, transformation equations involving the generalized hypergeometric function 3F2 are derived.
Experimental study on correlation between amplitude and phase of electromagnetic wave affected by time-varying plasma by amplitude-modulated radio frequency plasma generator
Authors: Yao Bo , Shi Lei , Li Xiaoping , Liu Yanming , Wei Hailiang
Published: April 2021

The time-varying plasma channel can increase the bit error rate of the phase modulation signal. The essential reason is that there is a correlation between the amplitude variation and phase variation caused by time-varying plasma. It can cause constellation rotation, and traditional communication methods cannot deal with this special interference. In this paper, the relationship between the amplitude and phase of electromagnetic wave affected by time-varying plasma is investigated. The correlation coefficient is derived. The result shows that the close correlation exists and the signs of correlation coefficients are different under different parameters. A verification experiment is also designed, and the time-varying transmission coefficients, constellations of QPSK signals, and correlation coefficients are measured under different conditions. The experimental results and the theoretical results are in good agreement. The conclusions can provide prior knowledge for communication methods and contribute to improving communication efficiency.
Effect of BaTiO3 nanowire on effective permittivity of the PVDF composites
Authors: Bai Pan , Wang Si-jiao , Jia Jian-jun , Wang Hong-xi , Yang Wei
Published: April 2021

With the increasing application of barium titanate (BaTiO3) in polyvinylidene fluoride (PVDF), the evaluation of its dielectric properties has attracted the attention of many frontier scholars. In this paper, from the theoretical point of view, the effects of the aspect ratio and the concentrations of BaTiO3 nanowires on macroscopic dielectric properties were studied by the finite element method. Depending on the calculation results, some conclusions had been obtained: First, it was found that the effect of higher aspect ratios of nanowires on the effective permittivity of the composites was not significant when the aspect ratio of the nanowire filler exceeded 20. Second, when the permittivity of the BaTiO3 nanowires reaches about 3000, as the permittivity of the filler increases, the rate of change of the effective permittivity of the composite material gradually slows down, which indicates that nanowires with higher permittivity have little influence on the effective permittivity of the composites. Finally, by comparing with permittivity data of BT/PVDF composites in the literature, it was found that the simulation results have good consistency with the experimentally measured values. The above-mentioned results have shown that the composite may exhibit good dielectric properties at a low concentration (<30 vol. %) and low permittivity filler. Moreover, the electrostatic field can roughly represent the electric field of a low-concentration composite under a certain electric field strength.
A tutorial in photoacoustic microscopy and tomography signal processing methods
Authors: Hysi Eno , Moore Michael J. , Strohm Eric M. , Kolios Michael C.
Published: April 2021

Over the last two and a half decades, photoacoustic (PA) imaging has become an important area of research in biomedical optics. Combining the high contrast of optical imaging with the high spatial resolution of ultrasound (US) imaging, PA imaging can simultaneously visualize anatomical structures while interrogating their functionality through multiwavelength optical spectroscopy. Alongside technological developments and imaging applications in optical and acoustic resolution PA imaging, a family of PA signal analysis techniques can extract additional information about the sample being imaged. This Tutorial focuses on techniques that rely on the analysis of PA signals in a manner similar to that in the complimentary field of quantitative ultrasound (QUS) imaging of soft tissues. In QUS, signal analysis techniques have been developed to analyze the US signals resulting from the scattering of many unresolved scatterers within the resolution volume of the imaging device. The implementation of these US techniques in PA can enable new applications in biomedicine beyond traditional anatomical PA imaging, further increasing the utilization and impact of this promising modality.
Application of slotted blade in the improvement of turbomachinery performance
Authors: Pan Xiong , Xinyuan Chen , Jianghong Deng , Liangcai Zeng , Feng Zhang
Published: April 2021

Flow separation is ubiquitous in turbomachinery. Compared with the more mature turbomachinery flow separation control method where the medium is gas, the turbomachinery flow separation method where the medium is liquid cannot be controlled well. In this study, according to the flow separation control principle of the aircraft fowler flap, taking the stator blade of the hydraulic torque converter as the basic research object, the stator blade shape is fitted with Joukowsky transformation, and then it is slotted. Computational fluid dynamics is used to perform flow analysis on original blades and slotted blades. It is found that compared with that of the original blade, the slotted blade’s flow separation phenomenon is effectively suppressed, turbulent kinetic energy is reduced, flow is more stable, and energy loss is reduced. In addition, using slotted blades for torque converter simulation, the torque ratio is increased by up to 0.245, and the efficiency is increased by up to 5%, which shows that slotted blades can improve the mechanical performance of the pump wheel and are not limited to the torque converter.
How adherence to public health measures shapes epidemic spreading: A temporal network model
Authors: Behring Brandon M. , Rizzo Alessandro , Porfiri Maurizio
Published: April 2021

The COVID-19 pandemic has laid bare the importance of non-pharmaceutical interventions in the containment of airborne infectious diseases. Social distancing and mask-wearing have been found to contain COVID-19 spreading across a number of observational studies, but a precise understanding of their combined effectiveness is lacking. An underdeveloped area of research entails the quantification of the specific role of each of these measures when they are differentially adopted by the population. Pursuing this research allows for answering several pressing questions like: how many people should follow public health measures for them to be effective for everybody? Is it sufficient to practice social distancing only or just wear a mask? Here, we make a first step in this direction, by establishing a susceptible–exposed–infected–removed epidemic model on a temporal network, evolving according to the activity-driven paradigm. Through analytical and numerical efforts, we study epidemic spreading as a function of the proportion of the population following public health measures, the extent of social distancing, and the efficacy of masks in protecting the wearer and others. Our model demonstrates that social distancing and mask-wearing can be effective in preventing COVID-19 outbreaks if adherence to both measures involves a substantial fraction of the population.
The effect of ion pairs on coacervate-driven self-assembly of block polyelectrolytes
Authors: Jiang Jiadi , Chen Er-Qiang , Yang Shuang
Published: April 2021

The incorporation of oppositely charged polyelectrolytes into a block copolymer system can lead to formation of microphase separated nanostructures driven by the electrostatic complex between two oppositely charged blocks. It is a theoretical challenge to build an appropriate model to handle such coacervate-driven self-assembly, which should capture the strong electrostatic correlations for highly charged polymers. In this paper, we develop the self-consistent field theory considering the ion paring effect to predict the phase behavior of block polyelectrolytes. In our model, two types of ion pairs, the binding between two oppositely charged monomers and the binding between charged monomers and counterions, are included. Their strength of formation is controlled by two parameters Kaa and Kac, respectively. We give a detailed analysis about how the binding strength Kac and Kaa and salt concentration affect the self-assembled nanostructure of diblock polyelectrolyte systems. The results show that the binding between two oppositely charged blocks provides driven force for microphase separation, while the binding between charged monomers and counterions competes with the polyion pairing and thus suppresses the microphase separation. The addition of salt has a shielding effect on the charges of polymers, which is a disadvantage to microphase separation. The phase diagrams as a function of polymer concentration and salt concentration at different situations are constructed, and the influence of Kaa, Kac, and charged block composition fa is analyzed in depth. The obtained phase diagrams are in good agreement with currently existing experimental and theoretical results.
Modeling the displacement speed in the flame surface density method for turbulent premixed flames at high pressures
Authors: Zhang Shiming , Lu Zhen , Yang Yue
Published: April 2021

We propose a model of the local displacement speed for the large-eddy simulation (LES) of turbulent premixed combustion with the flame surface density (FSD) method. This model accounts for flame stretch and curvature effects in order to improve the prediction of LES–FSD for turbulent premixed flames with the non-unity Lewis number at high pressures. The proposed model is validated by a priori and a posteriori tests, with the direct numerical simulation (DNS) and LES–FSD of statistically planar turbulent premixed flames of lean hydrogen at 1 and 10 atm and a range of turbulence intensities. The a priori test confirms that the proposed model accurately estimates the negative correlation of the displacement speed and the flame curvature. In the a posteriori test, the comparison of DNS and LES–FSD results demonstrates that the proposed model improves the prediction on the turbulent burning velocity and the turbulent flame thickness, compared with those from the existing displacement–speed model. The stretch effect in the present model leads to the rise of the turbulent burning velocity and the suppression of the “bending” phenomenon in LES–FSD, consistent with the DNS result.
Efficient hydrothermal growth of high-performance MoS2/pyramid-Si photocathodes by surface hydrophilicity engineering
Authors: Tu Baoxing , Weng Yuyan , Zheng Fengang , Su Xiaodong , Fang Liang , You Lu
Published: April 2021

Compared with traditional precious metal catalysts, MoS2 is regarded as the promising hydrogen evolution reaction catalyst for Si photocathodes, because of its higher photochemical stability and lower hydrogen adsorption free energy. However, the layers of MoS2 are connected by van der Waals force, and the interaction force between the layers of MoS2 and Si is weak. Therefore, the homogeneous MoS2 nanosheets directly synthesized on Si by the hydrothermal method remain challenging. Herein, we report a facile strategy for the fast and efficient growth of vertically standing MoS2 on pyramid Si via surface hydrophilicity tailoring by inserting a thin TiO2 layer. Thanks to the improved light trapping and catalytic kinetics, the optimal MoS2/TiO2/Si shows a short-circuit photocurrent density of 9.79 mA/cm2 and an onset potential of 0.31 V vs reversible hydrogen electrode under 100 mW/cm2 Xe-lamp illumination. By comparing with different oxide buffer layers, surface hydrophilicity is found to be essential for promoting the homogenous nucleation and growth of vertically standing MoS2 by the hydrothermal method. These results not only provide valuable insight into the growth kinetics of transition metal chalcogenides in aqueous solution but also deliver an efficient route for assembling noble-metal free catalysts on silicon-based photoelectrodes.
Cuprous or cupric? How substrate polarity can select for different phases of copper sulfide films in chemical bath deposition
Authors: Estrada Tania G. , Walker Amy V.
Published: April 2021

Copper sulfides have many applications from thermoelectrics to biotechnology. While the properties of different copper sulfide phases are well understood, controlling the deposited copper sulfide stoichiometry remains a significant challenge, especially in solution-phase synthesis techniques. In this work, we investigate the chemical bath deposition of CuxS on functionalized self-assembled monolayers (SAMs). Time-of-flight mass spectrometry, Raman spectroscopy, and x-ray photoelectron spectroscopy are employed to analyze the deposited films. We show that the use of thiourea as a sulfur source leads to the deposition of different copper sulfide phases and is controlled by the interaction of sulfur-containing ions in solution with the functionalized SAMs. For –COOH terminated SAMs, copper sulfide deposition is controlled by the surface polarity of the substrate. At the bath pH used in these experiments, the –COOH terminal groups are deprotonated. The resulting –COO− terminated SAM surface repels negatively charged sulfur-containing ions, leading to the deposition of Cu2S. For –CH3 terminated SAMs, which are non-polar, there is no specific interaction between the SAM terminal group and sulfur-containing ions and CuS is deposited. For –OH terminated SAMs, which have a polar terminal group, there are two competing effects: the repulsion of S-containing ions by the small negative charge of the terminal –OH group and the increase in the concentration of sulfur-containing ions in solution as the bath pH increases. This competition leads to the deposit stoichiometry changing from Cu2S at pH 9 to CuS at pH 12.
Identifying the structural relaxation dynamics in a strongly asymmetric binary glass former
Authors: Jin Xiao , Li Zijing , Liu Yingdan , Feng Shidong , Wang Li-Min
Published: April 2021

Here, we provide calorimetric and dielectric studies in asymmetric binary mixtures constituted by 2-picoline and triphenylethylene. Extreme broadening of the calorimetric glass transition is observed in the mixtures, which is accompanied by a large mismatch of the glass transition temperatures defined by the two techniques. As large broadening in the relaxation dispersion is identified in the mixtures of intermediate concentrations, strong temperature dependence of the relaxation dispersion is detected. The relation between the stretching exponent and non-linear factor derived from the Tool–Narayanaswamy–Moynihan–Hodge model shows a remarkable shift from the one established by pure molecular glass formers and symmetric mixtures. The unusual behaviors suggest an extreme dynamical decoupling mode imposed by the occurrence of strong concentration fluctuation.
Experimental investigation of elevation internal solitary wave propagation over a ridge
Authors: Du Hui , Wang Shao-Dong , Wang Xin-Long , Xu Jun-Nan , Guo Hai-long , Wei Gang
Published: April 2021

The propagation of elevation internal solitary waves (ISWs) over a large triangular ridge was investigated experimentally in a stratified fluid flume. The propagation characteristics of the elevation ISWs over the ridge were measured by using the real-time wave measuring instrument and particle image velocimetry, respectively. At the front slope of the ridge, the obvious fluid accumulation appeared, the waveform was distorted and broadened, the ISW amplitude increased slightly, the phase velocity decreased suddenly, and the lower layer flow velocity increased significantly. In the region of the ridge top, counterclockwise vortex and bright spots appeared, which signified the occurrence of breaking, the shape of incident wave was transferred to the shape of table-top solitary wave. At the back slope of the ridge, the fission waves became symmetric gradually and restored to normal, the amplitude decreased significantly, and the phase velocity increased slightly. The wave energy decreased consistently during wave propagation and the whole energy loss was about 30%–35% of the incident wave. Due to the wave breaking and fission, the energy loss occurred near the ridge top was the largest and was almost the same at symmetrical positions on the front and back slopes.
Improved low-frequency noise in CVD bilayer MoS2 field-effect transistors
Authors: Gao Qingguo , Zhang Chongfu , Yi Zichuan , Pan Xinjian , Chi Feng , Liu Liming , Li Xuefei , Wu Yanqing
Published: April 2021

In MoS2 field-effect transistors, the current or voltage fluctuations related to either mobility- or number-dependent relationships are characterized by low-frequency noise. This noise can typically be used to evaluate the application limits of MoS2-based electronic devices. In this work, the low-frequency noise characteristics of single-crystal bilayer MoS2 grown by chemical vapor deposition (CVD) are systematically investigated and found to offer significant performance improvements compared with those based on the monolayer MoS2 channel. At f = 100 Hz, the normalized drain current power spectral density (SI/Id2) is 2.4 × 10−10 Hz−1 and 3.1 × 10−9 Hz−1 for bilayer and monolayer MoS2 transistors, respectively. The 1/f noise behavior can be accurately described by McWhorter's carrier number fluctuation model for both transistor types, suggesting that carrier trapping and de-trapping by dielectric defects is the dominant mechanism of 1/f noise in CVD MoS2 transistors. Furthermore, a minimal WLSI/Id2 of 3.1 × 10−10 μm2/Hz (where W is the gate width and L is the gate length) is achieved at Vbg = 3 V by effectively reducing the contact resistance of bilayer MoS2 transistors using a back-gate voltage. These results demonstrate that CVD bilayer MoS2 is a promising candidate for future large-scale 2D-semiconductor-based electronic applications with improved noise performance.
Simulation of flow induced by single-dielectric-barrier-discharge plasma actuator using a high-order flux-reconstruction scheme
Authors: Zhao Longxiang , Xiao Zuoli , Liu Feng
Published: April 2021

The starting vortex flow generated by a single-dielectric-barrier-discharge (SDBD) plasma actuator in still air is investigated numerically by direct numerical simulation (DNS) using a 4th order Navier–Stokes solver and Suzen's model for the plasma actuator. The Navier–Stokes equations and the equations for the electric field and the charge density distribution in the plasma body force model are solved by the same high-order method based on the flux reconstruction algorithm on arbitrary mixed grids, allowing easy extension to configurations of complex geometry. The computational method and its high orders of accuracy are verified for the problem of the translation of an isentropic vortex and validated for the vortex shedding problem behind a circular cylinder. The plasma body force model is then implemented in the Navier–Stokes code to perform highly resolved DNS of the starting vortex generated by an SDBD plasma actuator. The computed vortex pattern and its trajectory with time are compared with available experimental data. The computational results confirm similarity laws on the motion of the vortex.
Two-layer modeling of thermally induced Bénard convection in thin liquid films: Volume of fluid approach vs thin-film model
Authors: Mohammadtabar Ali , Nazaripoor Hadi , Riad Adham , Hemmati Arman , Sadrzadeh Mohtada
Published: April 2021

This study focuses on a detailed analysis of thermally induced Bénard convection, thermocapillary instability, and interfacial deformation of a nanofilm. The dynamics, instability, and morphological evolution of a thin liquid film investigated using a volume of fluid (VOF) numerical scheme that incorporates the Marangoni stress to model the gas–liquid interface deformation. The results obtained from VOF are then compared with those of the “thin-film” model in many cases to find an accurate model for predicting the characteristic wavelength for the growth of instabilities. We also present a correlation to predict the relation between the characteristic wavelength found by VOF numerical results and the analytical linear stability analysis predictions. This is followed by examining the protrusion width and the distance between the protrusions on the structures’ final shape and interface evolution time. Finally, linear theoretical relations for the formation of secondary pillars are presented based on the width of protrusions, their separation distance, and the inverse filling ratio. The results show that the number of pillars increases when the width and distance between two protrusions are greater than a critical value.
Axis-dependent carrier polarity in polycrystalline NaSn2As2
Authors: Nakamura Naoto , Goto Yosuke , Mizuguchi Yoshikazu
Published: April 2021

Transverse thermoelectric devices consist of only one thermoelectric material, unlike conventional longitudinal thermoelectric devices that require two types of thermoelectric materials with p- and n-type polarities. However, scalable synthesis of materials that demonstrate axis-dependent carrier polarity, which is a prospective component to demonstrate the transverse thermoelectric device, is challenging. This paper reports that polycrystalline NaSn2As2, which was prepared by using uniaxial hot pressing, displayed axis-dependent carrier polarity. The preferred orientation of the sample was confirmed through x-ray diffraction measurements. Seebeck coefficient measurements indicate that carrier polarity depends on the measurement direction, which is consistent with recently reported results on single crystals of NaSn2As2. Given that our sample preparation procedure is readily scalable, the present work shows the possibility for preparing transverse thermoelectric devices using polycrystalline NaSn2As2 with a preferred orientation.
Mechanism of periodic field driven self-assembly process
Authors: Xu Duo , Shi Rui , Sun Zhao-Yan , Lu Zhong-Yuan
Published: April 2021

Dissipative self-assembly, a ubiquitous type of self-assembly in biological systems, has attracted a lot of attention in recent years. Inspired by nature, dissipative self-assembly driven by periodic external fields is often adopted to obtain controlled out-of-equilibrium steady structures and materials in experiments. Although the phenomena in dissipative self-assembly have been discovered in the past few decades, fundamental methods to describe dynamical self-assembly processes and responsiveness are still lacking. Here, we develop a theoretical framework based on the equations of motion and Floquet theory to reveal the dynamic behavior changing with frequency in the periodic external field driven self-assembly. Using the dissipative particle dynamics simulation method, we then construct a block copolymer model that can self-assemble in dilute solution to confirm the conclusions from the theory. Our theoretical framework facilitates the understanding of dynamic behavior in a periodically driven process and provides the theoretical guidance for designing the dissipative conditions.
External pressure dependence of granular orifice flow: Transition to Beverloo flow
Authors: Peng Zheng , Zhou Jiangmeng , Zhou Jiahao , Miao Yuan , Cheng Liyu , Jiang Yimin , Hou Meiying
Published: April 2021

In this paper, we have designed and employed a suspended-wall silo to remove the Janssen effect in order to explore directly the local pressure dependence of granular orifice flow (GOF) systematically. We find that as the Janssen effect is removed, the flow rate Q changes linearly with the external pressure. The slope α of the linear change decays exponentially with the ratio of the silo size and the size of the orifice Φ/D, which suggests the existence of a characteristic ratio λ (∼2.4). When Φ/D > λ, α gradually decays to zero, and the effect of external pressure on the GOF becomes negligible, where the Beverloo law retrieves. Our results show that the Janssen effect is not a determining factor of the constant rate of GOF, although it may contribute to shield the top load. The key parameter in GOF is Φ/D. In small Φ/D, the flow rate of GOF can be directly adjusted by the external pressure via our suspended-wall setup, which may be useful to the transportation of granules in microgravity environment where the gravity-driven Beverloo law is disabled.
A magnetic domain wall Mackey–Glass oscillator
Authors: Williame Jérôme , Kim Joo-Von
Published: April 2021

We propose a time-delay oscillator using Mackey–Glass nonlinearity based on a pinned magnetic domain wall in a thin film nanostrip. Through spin transfer torques, electric currents applied along the strip cause the domain wall to deform and displace away from a geometrical pinning site, which can be converted into a nonlinear transfer function through a suitable choice of a readout. This readout serves as a delay signal, which is subsequently fed back into the applied current with amplification. With micromagnetics simulations, we study the role of the readout position, time delay, and feedback gain on the dynamics of this domain wall. In particular, we highlight regimes in which self-sustained oscillations and complex transients are possible.
Microscopic reversibility demands lower open circuit voltage in multiple exciton generation solar cells
Authors: Pusch Andreas , Bremner Stephen P. , Tayebjee Murad J. Y. , Daukes Nicholas J. Ekins
Published: April 2021

Multiple exciton generation (MEG) increases the short circuit current of solar cells and is, therefore, often cited as a candidate scheme for surpassing the efficiency limit of single junction solar cells. Conventionally, limiting efficiencies for MEG solar cells have been calculated using quasi-equilibrium models that implicitly assume an effective separation of timescales between different processes. We show here that this separation of timescales is not possible for MEG solar cells, with Auger recombination, the inverse process to multi-exciton generation, needing to be considered explicitly in the efficiency limits of an MEG solar cell. We assess the impact of Auger recombination using a non-equilibrium model of a quantum dot solar cell that satisfies microscopic reversibility and can approximate experimental external quantum efficiency (EQE) curves of MEG solar cells. Recombination—both Auger and radiative—is treated in a quasi-equilibrium approach, which can be justified with a clear model for the separation of timescales. A key insight of this model is that the achievable voltage of the device, and hence the solar energy conversion efficiency, depends on the absolute values of the impact ionization rate and the rate at which electrons lose energy through phonon scattering. By contrast, the EQE profile at short circuit depends only on the ratio of these two rates. This shows that the potential of certain MEG solar cell approaches cannot be assessed from EQE improvements alone, which highlights the importance of considering non-equilibrium processes in models of solar energy conversion devices.
Manifolds of isospectral arrow matrices
Authors: Ayzenberg A. A. , Buchstaber V. M.
Published: April 2021

An arrow matrix is a matrix with zeros outside the main diagonal, the first row and the first column. We consider the space

of Hermitian arrow

-matrices with fixed simple spectrum

. We prove that this space is a smooth

-manifold with a locally standard torus action: we describe the topology and combinatorics of its orbit space. If

, the orbit space

is not a polytope, hence

is not a quasitoric manifold. However, there is an action of a semidirect product

on

, and the orbit space of this action is a certain simple polytope

obtained from the cube by cutting off codimension-2 faces. In the case

, the space

is a solid torus with boundary subdivided into hexagons in a regular way. This description allows us to compute the cohomology ring and equivariant cohomology ring of the 6-dimensional manifold

and another manifold, its twin.

Bibliography: 32 titles.
Multivariate Haar systems in Besov function spaces
Authors: Oswald P.
Published: April 2021

We determine all cases for which the-dimensional Haar wavelet systemon the unit cubeis a conditional or unconditional Schauder basis in the classical isotropic Besov function spaces,,, defined in terms of first-order-moduli of smoothness. We obtain similar results for the tensor-product Haar system, and characterize the parameter range for which the dual ofis trivial for.

Bibliography: 31 titles.
The preservation of threshold resonances and the splitting off of eigenvalues from the threshold of the continuous spectrum of quantum waveguides
Authors: Nazarov S. A.
Published: April 2021

Threshold resonance arises on the lower bound of the continuous spectrum of a quantum waveguide (the Dirichlet problem for the Laplace operator), provided that for this value of the spectral parameter a nontrivial bounded solution exists which is either a trapped wave decaying at infinity or an almost standing wave stabilizing at infinity. In many problems in asymptotic analysis, it is important to be able to distinguish which of the waves initiates the threshold resonance; in this work we discuss several ways to clarify its properties. In addition, we demonstrate how the threshold resonance can be preserved by fine tuning the profile of the waveguide wall, and we obtain asymptotic expressions for the near-threshold eigenvalues appearing in the discrete or continuous spectrum when the threshold resonance is destroyed.

Bibliography: 60 titles.
Characterization of solutions of strong-weak convex programming problems
Authors: Dudov S. I. , Osiptsev M. A.
Published: April 2021

Finite-dimensional problems of minimizing a strongly or weakly convex function on a strongly or weakly convex set are considered. Necessary and sufficient conditions for solutions of such problems are presented, which are based on estimates for the behaviour of the objective function on the feasible set taking account of the parameters of strong or weak convexity, as well as certain local features of the set and the function. The mathematical programming problem is considered separately for strongly and weakly convex functions. In addition, necessary conditions for a global and a local solution with differentiable objective function are found, in which a ‘strong’ stationarity condition is assumed to hold.

Bibliography: 33 titles.
A trace formula for higher order ordinary differential operators
Authors: Gal’kovskii E. D. , Nazarov A. I.
Published: April 2021

We obtain a first-order trace formula for a higher order differential operator on a closed interval in the case where the perturbation operator is the operator of multiplication by a finite complex-valued charge. For operators of even orders

, the result contains a term of new type, previously unknown.

Bibliography: 15 titles.
Recovery of integrable functions and trigonometric series
Authors: Plotnikov M. G.
Published: April 2021

Classes

of

-functions with fixed rate of decrease of their Fourier coefficients are considered. For each class

, it is shown that there exists a (recovery) set

with arbitrarily small measure such that any function in

can be recovered from its values on

. A formula for evaluation of the Fourier coefficients of such a function from its values on

is given. In addition, it is shown that, for any

-function, a function-specific recovery set can be found. The problem of recovery of general trigonometric series from the Zygmund classes which converge to summable functions on such sets

is also solved.

Bibliography: 10 titles.
Emergence of hierarchy in networked endorsement dynamics
Authors: Kawakatsu Mari , Chodrow Philip S. , Eikmeier Nicole , Larremore Daniel B.
Published: April 2021

Significance

Hierarchies structure the lives of many social animals, including humans. We propose a generative model of time-varying networks in which endorsements between individuals give rise to enduring hierarchies. For several network-based ranking functions, our model possesses a distinct, analytically tractable, critical transition between egalitarian and hierarchical states. We also use our model to explore hierarchical structures in empirical data on hiring patterns among mathematicians, dominance relations among parakeets, and friendships among members of a fraternity, observing several persistent patterns. Overall, our model enables data-informed modeling of hierarchical networks in social and biological systems.
Brd4-bound enhancers drive cell-intrinsic sex differences in glioblastoma
Authors: Kfoury Najla , Qi Zongtai , Prager Briana C. , Wilkinson Michael N. , Broestl Lauren , Berrett Kristopher C. , Moudgil Arnav , Sankararaman Sumithra , Chen Xuhua , Gertz Jason , Rich Jeremy N. , Mitra Robi D. , Rubin Joshua B.
Published: April 2021

Significance

Consistent sex differences in incidence and outcome have been reported in numerous cancers including brain tumors. GBM, the most common and aggressive primary brain tumor, occurs with higher incidence and shorter survival in males compared to females. Brd4 is essential for regulating transcriptome-wide gene expression and specifying cell identity, including that of GBM. We report that sex-biased Brd4 activity drives sex differences in GBM and renders male and female tumor cells differentially sensitive to BET inhibitors. The observed sex differences in BETi treatment strongly indicate that sex differences in disease biology translate into sex differences in therapeutic responses. This has critical implications for clinical use of BET inhibitors further affirming the importance of inclusion of sex as a biological variable.
De novo biosynthesis of a nonnatural cobalt porphyrin cofactor inE. coliand incorporation into hemoproteins
Authors: Perkins Lydia J. , Weaver Brian R. , Buller Andrew R. , Burstyn Judith N.
Published: April 2021

Significance

Enzymes rely on cofactors, both organic molecules and metal ions, for reactivity beyond what can be performed with the 20 standard amino acids. One way to expand the reactivity of heme-dependent proteins is to swap the native iron atom in the heme cofactor for a different metal. Because the resulting metal-containing cofactor is new to nature, methods for producing these nonnative hemoproteins are difficult and often limited to the test tube. Here, we report a method for subverting the heme biosynthetic pathway inE. colito produce cobalt protoporphyrin IX (CoPPIX) and CoPPIX-substituted hemoproteins in living cells. This method enables the use of CoPPIX-substituted enzymes as biocatalysts and widens the scope of proteins that may be studied by metal substitution.
Repeated mutation of a developmental enhancer contributed to human thermoregulatory evolution
Authors: Aldea Daniel , Atsuta Yuji , Kokalari Blerina , Schaffner Stephen F. , Prasasya Rexxi D. , Aharoni Adam , Dingwall Heather L. , Warder Bailey , Kamberov Yana G.
Published: April 2021

Significance

One of the most distinctive physiological traits differentiating humans from other primates is a reliance on sweating to cool off. The effectiveness of human thermoregulatory sweating is underlain by the evolution of a dramatically increased density of water-secreting eccrine sweat glands in human skin relative to that of other primates. Here, we show that the accumulation of human-specific mutations in a developmental enhancer collectively promoted the production of eccrine glands in humans by up-regulating the expression of the
Engrailed 1
transcription factor in the skin. This study reveals a mechanism that contributed to the evolution of humans’ signature thermoregulatory capabilities and underscores the importance of regulatory evolution in generating the modern human form.
Reduced phase stability and faster formation/dissociation kinetics in confined methane hydrate
Authors: Jin Dongliang , Coasne Benoit
Published: April 2021

Significance

Large amounts of methane hydrate—which consists of water forming molecular ice cages around methane molecules—are trapped in the porosity of rocks and seafloors. The impact of this so-called “burning ice” on our environment remains unclear (methane is a potent greenhouse gas), especially the parameters driving its phase stability and kinetics. Here, using molecular modeling, we identify the mechanisms involved in the formation/dissociation of confined methane hydrate. The phase stability of confined methane hydrate is shown to be restricted to a narrower temperature/pressure range with faster underlying formation/dissociation kinetics. Such facilitated freezing, which helps rationalize experimental observations, is described using a mesoscale thermodynamic approach of the nucleation mechanism.
The role of annealing in determining the yielding behavior of glasses under cyclic shear deformation
Authors: Bhaumik Himangsu , Foffi Giuseppe , Sastry Srikanth
Published: April 2021

Significance

Understanding the nature of the yielding transition in amorphous solids is of significant interest conceptually and for practical reasons. We use computer simulations of models of silica—a network glass—and an atomic glass to investigate the effect of annealing on yielding under cyclic shear deformation. We identify a threshold energy toward which poorly annealed glasses evolve as yielding is approached under cyclic deformation, and below which glasses display little change until they yield, with progressively stronger discontinuities as degree of annealing increases. The threshold energy thus separates two distinct regimes of yielding, with increasingly brittle behavior at lower energies. Interestingly, the threshold energy corresponds to well-studied dynamical cross-overs in the corresponding liquids.
A model for a partnership of lipid transfer proteins and scramblases in membrane expansion and organelle biogenesis
Authors: Ghanbarpour Alireza , Valverde Diana P. , Melia Thomas J. , Reinisch Karin M.
Published: April 2021

The autophagy protein ATG2, proposed to transfer bulk lipid from the endoplasmic reticulum (ER) during autophagosome biogenesis, interacts with ER residents TMEM41B and VMP1 and with ATG9, in Golgi-derived vesicles that initiate autophagosome formation. In vitro assays reveal TMEM41B, VMP1, and ATG9 as scramblases. We propose a model wherein membrane expansion results from the partnership of a lipid transfer protein, moving lipids between the cytosolic leaflets of apposed organelles, and scramblases that reequilibrate the leaflets of donor and acceptor organelle membranes as lipids are depleted or augmented. TMEM41B and VMP1 are implicated broadly in lipid homeostasis and membrane dynamics processes in which their scrambling activities likely are key.
An ultra-high-affinity small organic ligand of fibroblast activation protein for tumor-targeting applications
Authors: Millul Jacopo , Bassi Gabriele , Mock Jacqueline , Elsayed Abdullah , Pellegrino Christian , Zana Aureliano , Dakhel Plaza Sheila , Nadal Lisa , Gloger Andreas , Schmidt Eleonore , Biancofiore Ilaria , Donckele Etienne J. , Samain Florent , Neri Dario , Cazzamalli Samuele
Published: April 2021

Significance

Fibroblast activation protein (FAP) has recently emerged as a tumor-associated antigen with abundant and selective expression in the majority of human solid malignancies. To the best of our knowledge, OncoFAP is the highest-affinity small organic FAP ligand reported to date, with a dissociation constant of 680 pM, as measured by fluorescence polarization. Upon intravenous administration, both fluorescent and radiolabeled OncoFAP derivatives exhibited a rapid and selective accumulation in FAP-positive tumors, sparing normal tissues. OncoFAP was also used as a modular component for the generation of therapeutic products, enabling the targeted delivery of a potent beta-emitter (lutetium-177), of fluorescein-specific chimeric antigen receptor (CAR) T cells or of highly cytotoxic auristatin derivatives to FAP-positive tumors in vitro and in vivo.