bluuebunny/crossref_metadata_2025 huggingface dataset:
Stabilization of Néel-type domain walls in multilayered magnetic wires using antiferromagnetic interlayer exchange coupling
Authors: Tanaka Masaaki , Shimazaki Musashi , Ohmasa Tatsuro , Suzuki Takafumi , Honda Shunsuke , Honda Syuta , Awano Hiroyuki , Mibu Ko
Published: August 2020

We investigated the relation between the domain wall (DW) configuration and the strength of the interlayer exchange coupling (IEC) in multilayered magnetic wires, where a Ru spacer layer mediates the IEC between two ferromagnetic layers, and a Pt cap layer contributes to the interfacial Dzyaloshinskii–Moriya interaction. It was found that the antiferromagnetic IEC stabilizes the Néel-type DWs in the wires and that the stability varies with the strength of the antiferromagnetic IEC. The micromagnetic simulations imply that the Néel-type DWs are stabilized because the rotation of the magnetic moments in the DWs is restricted in the antiferromagnetically coupled ferromagnetic layers.
Generalized Schrödinger equations with quadratical energy-dependence in the potential: Darboux transformations and application to the Heun class
Authors: Schulze-Halberg Axel
Published: August 2020

We construct Darboux transformations of arbitrary order for generalized Schrödinger-type equations, the potentials of which are second-degree polynomials in the energy. Our equations are allowed to contain first-derivative terms with arbitrary coefficients, such as they occur, for example, in position-dependent mass scenarios. Our Darboux transformations are shown to be applicable to equations from the Heun class.
Hybrid anisotropic pentamode mechanical metamaterial produced by additive manufacturing technique
Authors: Mohammadi Kaivan , Movahhedy Mohammad R. , Shishkovsky Igor , Hedayati Reza
Published: August 2020

Pentamode metamaterials are a type of extremal designer metamaterials, which are able to demonstrate extremely high rigidity in one direction and extremely high compliance in other directions. Pentamodes can, therefore, be considered as building blocks of exotic materials with any arbitrarily selected thermodynamically admissible elasticity tensor. The pentamode lattices can then be envisioned to be combined to construct intermediate extremal materials, such as quadramodes, trimodes, and bimodes. In this study, we constructed several primary types of anisotropic pentamode lattices (with midpoint positioning of 10%, 15%, 20%, 25%, 30%, 35%, and 42% of the main unit cell diagonal) and then combined them mutually to explore the dependence of elastic properties of hybrid pentamodes on those of individual constructing lattices. Several anisotropic individual and hybrid pentamode lattice structures were produced using the MultiJet Additive Manufacturing technique and then mechanically tested under compression. Finite element models were also created using the COMSOL Multiphysics package. Two-component hybrid pentamode lattices composed of individual lattices with extensively different (as large as two orders of magnitudes) B/G ratios were constructed and analyzed. It was demonstrated that it is possible to design and construct composite intermediate extremal materials with arbitrary eigenvalues in the elastic tensor. It is concluded that the elastic E, shear G, and bulk moduli B of the hybrid structure are the superpositions of the corresponding moduli of the individual lattice structures. Poisson's ratio ν of the hybrid pentamode structure equals that of individual structure with higher Poisson's ratio. The yield stress σy of the hybrid pentamode lattice structure depends on the elastic moduli of the constructing lattice structures, as well as the yield stress of the weaker lattice structure.
Enhancement of harvesting capability of coupled nonlinear energy harvesters through high energy orbits
Authors: Malaji P. V. , Friswell M. I. , Adhikari S. , Litak G.
Published: August 2020

Mechanical coupling in similar energy harvesters has the potential to enhance their broadband harvesting capability. However, often the performance of one harvester dominates the other, and the coupling transfers energy from the high frequency harvester to the low frequency harvester, thus reducing the capability of the high frequency harvester. Hence, researchers have proposed using the high frequency harvester only as an auxiliary oscillator to save the material cost. This paper investigates the possibility of enhancing the energy harvesting capability of both coupled harvesters. A torsionally coupled electromagnetic pendulum harvester system is considered, which is suitable for low frequency (<5 Hz) applications. The harmonic balance method is used to identify possible multiple solutions, and high magnitude solutions are observed to coexist with low magnitude solutions. These high energy solutions, which are often missed in the numerical simulation, can be attained by a careful choice of initial conditions or energy input. The simulation results show that more energy can be harvested over a wider range of frequencies by ensuring that the response occurs in the high energy orbits. The results show an enhancement of the bandwidth by 54% and 140% for the low and high frequency harvesters, respectively, with the optimum initial conditions. Moreover, an isolated frequency island is reported, which occurs due to the coupling of the nonlinear harvesters.
Role of dynamical compressive and shear loading on hotspot criticality in RDX via reactive molecular dynamics
Authors: Islam Md Mahbubul , Strachan Alejandro
Published: August 2020

Energy localization in hotspots due to shock-induced pore collapse is thought to be a critical process in the initiation of heterogeneous high-energy density materials. The dynamical collapse of porosity involves expansion, jetting, shearing, and recompression of the material surrounding the defect. While the resulting hotspots are known to result in deflagration waves that can lead to detonation, we lack the understanding of the relative potency of the various processes that occur during the collapse. We use molecular dynamics simulations with the reactive force field ReaxFF to characterize how uniaxial expansion/recompression, shear, and combinations thereof affect the formation and criticality of hotspots in RDX, 1,3,5-trinitro-1,3,5-triazine. We chose a planar pore configuration consisting of a 40 nm gap and independently control the relative amounts of compressive and shear shock loadings. We find that shear-dominated critical hotspots tend to be smaller but exhibit higher temperatures than uniaxial ones and involve longer reaction time scales. Interestingly, the chemical decomposition mechanisms are affected by the relative amount of dynamical shear and uniaxial loads.
Rarefied gas flow past a flat plate at zero angle of attack
Authors: Abramov A. A. , Butkovskii A. V. , Buzykin O. G.
Published: August 2020

We consider subsonic, transonic, and moderate supersonic rarefied monatomic gas flows past a flat plate at zero angle of attack in the transitional regime. The influence of the rarefaction on the flow pattern is investigated mainly by the direct simulation Monte Carlo method. We study the shear stress, normal momentum flux transferred to the plate, and energy flux transferred to the plate at various Knudsen numbers, Mach numbers, and plate temperatures. We show that if the plate temperature is equal to the temperature of the undisturbed gas, then at any Mach number of the incoming flow, the average dimensionless normal momentum transferred to the plate has at least one extreme with respect to the Knudsen number. Specifically, in the supersonic and sonic cases, these dependences have a maximum. In the case of subsonic transonic Mach number M = 0.8, the dependence has a weak maximum and a weak minimum. At M = 0.5, it has weak minimum. We show that in a wide temperature range at subsonic and moderate supersonic Mach numbers in the transitional regime, the plate temperature very weakly affects the average friction force acting on the plate. We show that there exist certain intervals of plate temperatures ratios and Mach numbers such that the average dimensionless energy flux transferred to the plate changes the sign if the Knudsen number increases, previously reaching a local negative minimum.
Effect of inflow temperature on root canal irrigation: A computational fluid dynamics study
Authors: Yu Mingzhou , Huang Zhengqiu , Zhou Na , Xu Zihan , Deng Shuli , Jin Hanhui
Published: August 2020

Root canal therapy is one of the main treatment options for endodontic diseases in which an effective irrigation is key to a successful therapy. In the present paper, the irrigation flow inside an instrumented root canal is numerically investigated, and then the effect of inflow temperature on the irrigation is analyzed based on the computational fluid dynamics results. The magnitude of the shear stress and its corresponding coverage of the irrigation flow on the wall is adopted to characterize the clean efficiency. The axial velocity is used to represent the replacement of local flow field, which stands for the capability to carry away the cleaning residue. Results show that the effective area that the shear stress covers on the root canal wall behind the needle outlet is usually larger than that in front of the outlet, and both the effective coverage of the shear stress and the replacement of the irrigant are improved when the velocity increases. It is convinced that the critical shear stress, namely, the lowest shear stress required to peel off the smear layer on the root canal wall, decreases with the increase in the temperature. Although no apparent variation of the shear stress on the wall can be observed while improving the inflow temperature, the effective surface to be cleaned is improved to some extent because of the decrease in the critical shear stress. Meanwhile, the power consumption is reduced obviously. If the input power remains constant when the temperature increases, both the shear stress on the wall and the replacement are significantly improved besides the decrease in the critical shear stress. This means both the clean efficiency on the wall and the clearing capability (namely replacement) in local flow field are significantly promoted.
Toward high efficiency tin perovskite solar cells: A perspective
Authors: Li Hansheng , Wei Qi , Ning Zhijun
Published: August 2020

The development of high-performance lead-free perovskite solar cells (PSCs) is important to address the environmental concern of lead perovskite. In recent years, tin perovskite solar cells (TPSCs) have been developing quickly and emerging as a promising candidate for high-efficiency lead-free PSCs. In this Perspective, we summarize recent work of our group including the use of a low-dimensional structure, film growth kinetic control, and device engineering. In the end, the challenges in TPSCs and potential strategies toward high-efficiency TPSCs are discussed.
Jeffery orbits for an object with discrete rotational symmetry
Authors: Ishimoto Kenta
Published: August 2020

We theoretically investigate the motions of an object immersed in a background flow at a low Reynolds number, generalizing the Jeffery equation for the angular dynamics to the case of an object with n-fold rotational symmetry (n ≥ 3). We demonstrate that when n ≥ 4, the dynamics are identical to those of a helicoidal object for which two parameters related to the shape of the object, namely, the Bretherton constant and a chirality parameter, determine the dynamics. When n = 3, however, we find that the equations require a new parameter that is related to the shape and represents the strength of triangularity. On the basis of detailed symmetry arguments, we show theoretically that microscopic objects can be categorized into a small number of classes that exhibit different dynamics in a background flow. We perform further analyses of the angular dynamics in a simple shear flow, and we find that the presence of triangularity can lead to chaotic angular dynamics, although the dynamics typically possess stable periodic orbits, as further demonstrated by an example of a triangular object. Our findings provide a comprehensive viewpoint concerning the dynamics of an object in a flow, emphasizing the notable simplification of the dynamics resulting from the symmetry of the object’s shape, and they will be useful in studies of fluid–structure interactions at a low Reynolds number.
Light-emitting diodes with AlN polarization-induced buried tunnel junctions: A second look
Authors: Lee Kevin , Bharadwaj Shyam , Shao Yu-Tsun , van Deurzen Len , Protasenko Vladimir , Muller David A. , Xing Huili Grace , Jena Debdeep
Published: August 2020

Interband Zener tunneling of electrons has been recently used in III-nitride semiconductor based light emitters to efficiently inject holes into p-cladding layers. Zener tunneling probabilities can be significantly enhanced if crystal symmetry-induced internal polarization fields assist the dopant-induced built-in electric fields of tunnel junctions because of the large reduction of the tunneling distance. In a metal-polar buried tunnel junction geometry, such electric field alignment needs an AlN interlayer at the tunnel junction. Because AlN is a larger bandgap semiconductor than GaN, it is not clear a priori if the net tunneling probability is reduced or enhanced compared to a homojunction. By combining theoretical modeling with experimental blue light emitting diodes, we find that the large tunneling enhancement due to the polarization field and band realignment overcome the reduction in tunneling due to the larger bandgap of AlN. Compared to a homojunction tunnel-junction, the inclusion of AlN in the tunnel junction is found to lower the turn-on and operating voltages and increase the wall-plug efficiency. This proves that polarization-induced AlN tunnel junctions are superior to homojunctions at low injection currents, resulting in higher optical emission intensity and superior uniformity.
Chemical treatment effects on Schottky contacts to metalorganic chemical vapor deposited n-type N-polar GaN
Authors: Khachariya Dolar , Szymanski Dennis , Sengupta Rohan , Reddy Pramod , Kohn Erhard , Sitar Zlatko , Collazo Ramón , Pavlidis Spyridon
Published: August 2020

In this work, we investigate the effect of different chemical treatments, such as solvents, bases, and acids, on the surface properties and electrical behavior of Schottky diodes fabricated on metalorganic chemical vapor deposition-grown, n-type, N-polar GaN. The I–V and C–V barrier heights of the as-grown Schottky diodes are found to be 0.40 eV and 0.60 eV, respectively, with an ideality factor n = 1.07. It is found that the solvent treatments neither change the surface nor the electrical performance of the Schottky diodes, as expected. However, the treatments by the alkaline photolithography developer and acid—the latter of which is often used to clean the surface of Ga-polar GaN films prior to metal contact deposition—degrade the performance of N-polar GaN. These base and acid treatments severely roughen the surface by creating triangular/hexagonal crystallographic facets. The I–V and C–V barrier heights of these base- and acid-treated diodes are increased to 0.63 eV and 1.00 eV, respectively, with ideality factor values n < 1.2. X-ray photoelectron spectroscopy studies indicate that base- and acid-treated surfaces have lower oxygen content as compared to the as-grown sample surface. It is understood that the increment in the barrier height for base- and acid-treated diodes could be due to the change in polarity, from N-polar to semi-polar/non-polar, on these crystallographic features. All these results demonstrate that, unlike for Ga-polar GaN, the N-polar GaN surface is highly reactive to bases and acids.
A Gaussian process regression adaptive density guided approach for potential energy surface construction
Authors: Schmitz Gunnar , Klinting Emil Lund , Christiansen Ove
Published: August 2020

We present a new iterative scheme for potential energy surface (PES) construction, which relies on both physical information and information obtained through statistical analysis. The adaptive density guided approach (ADGA) is combined with a machine learning technique, namely, the Gaussian process regression (GPR), in order to obtain the iterative GPR–ADGA for PES construction. The ADGA provides an average density of vibrational states as a physically motivated importance-weighting and an algorithm for choosing points for electronic structure computations employing this information. The GPR provides an approximation to the full PES given a set of data points, while the statistical variance associated with the GPR predictions is used to select the most important among the points suggested by the ADGA. The combination of these two methods, resulting in the GPR–ADGA, can thereby iteratively determine the PES. Our implementation, additionally, allows for incorporating derivative information in the GPR. The iterative process commences from an initial Hessian and does not require any presampling of configurations prior to the PES construction. We assess the performance on the basis of a test set of nine small molecules and fundamental frequencies computed at the full vibrational configuration interaction level. The GPR–ADGA, with appropriate settings, is shown to provide fundamental excitation frequencies of an root mean square deviation (RMSD) below 2 cm−1, when compared to those obtained based on a PES constructed with the standard ADGA. This can be achieved with substantial savings of 65%–90% in the number of single point calculations.
Superconducting and antiferromagnetic properties of dual-phase V3Ga
Authors: Jamer Michelle E. , Wilfong Brandon , Buchelnikov Vasiliy D. , Sokolovskiy Vladimir V. , Miroshkina Olga N. , Zagrebin Mikhail A. , Baigutlin Danil R. , Naphy Jared , Assaf Badih A. , Lewis Laura H. , Pulkkinen Aki , Barbiellini Bernardo , Bansil Arun , Heiman Don
Published: August 2020

The binary compound V3Ga can exhibit two near-equilibrium phases, the A15 structure that is superconducting and the Heusler D03 structure that is semiconducting and antiferromagnetic. Density functional theory calculations show that these two phases are nearly degenerate, being separated in energy by only ±10 meV/atom. Our magnetization measurements on bulk-grown samples show antiferromagnetism and superconducting behavior below 14 K. These results indicate the possibility of using V3Ga for quantum technology devices exploiting the co-existence of superconductivity and antiferromagnetism in a dual-phase material.
Fractional diffusion on the human proteome as an alternative to the multi-organ damage of SARS-CoV-2
Authors: Estrada Ernesto
Published: August 2020

The coronavirus 2019 (COVID-19) respiratory disease is caused by the novel coronavirus SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), which uses the enzyme ACE2 to enter human cells. This disease is characterized by important damage at a multi-organ level, partially due to the abundant expression of ACE2 in practically all human tissues. However, not every organ in which ACE2 is abundant is affected by SARS-CoV-2, which suggests the existence of other multi-organ routes for transmitting the perturbations produced by the virus. We consider here diffusive processes through the protein–protein interaction (PPI) network of proteins targeted by SARS-CoV-2 as an alternative route. We found a subdiffusive regime that allows the propagation of virus perturbations through the PPI network at a significant rate. By following the main subdiffusive routes across the PPI network, we identify proteins mainly expressed in the heart, cerebral cortex, thymus, testis, lymph node, kidney, among others of the organs reported to be affected by COVID-19.
Experimental study of breathers and rogue waves generated by random waves over non-uniform bathymetry
Authors: Wang A. , Ludu A. , Zong Z. , Zou L. , Pei Y.
Published: August 2020

We present experimental evidence of formation and persistence of localized waves, breathers, and solitons, occurring in a random sea state and uniformly traveling over non-uniform bathymetry. Recent studies suggest connections between breather dynamics and irregular sea states and between extreme wave formation and breathers, random sea states, or non-uniform bathymetry individually. In this paper, we investigate the joint connection between these phenomena, and we found that breathers and deep-water solitons can persist in more complex environments. Three different sets of significant heights have been generated within a Joint North Sea Wave Observation Project wave spectrum, and the wave heights were recorded with gauges in a wave tank. Statistical analysis was applied to the experimental data, including the space and time distribution of kurtosis, skewness, Benjamin–Feir index, moving Fourier spectra, and probability distribution of wave heights. Stable wave packages formed out of the random wave field and traveling over shoals, valleys, and slopes were compared with exact solutions of the nonlinear Schrödinger equation with a good match, demonstrating that these localized waves have the same structure as deep-water breathers. We identify the formation of rogue waves at moments and over regions where the kurtosis and skewness have local maxima. These results provide insights for understanding of the robustness of Peregrine and higher-order Akhmediev breathers, Kuznetsov–Ma solitons, and rogue waves, and their occurrence in realistic oceanic conditions, and may motivate analogous studies in other fields of physics to identify limitations of exact weakly nonlinear models in non-homogeneous media.
Time-resolved resonant elastic soft x-ray scattering at Pohang Accelerator Laboratory X-ray Free Electron Laser
Authors: Jang Hoyoung , Kim Hyeong-Do , Kim Minseok , Park Sang Han , Kwon Soonnam , Lee Ju Yeop , Park Sang-Youn , Park Gisu , Kim Seonghan , Hyun HyoJung , Hwang Sunmin , Lee Chae-Soon , Lim Chae-Yong , Gang Wonup , Kim Myeongjin , Heo Seongbeom , Kim Jinhong , Jung Gigun , Kim Seungnam , Park Jaeku , Kim Jihwa , Shin Hocheol , Park Jaehun , Koo Tae-Yeong , Shin Hyun-Joon , Heo Hoon , Kim Changbum , Min Changi-Ki , Han Jang-Hui , Kang Heung-Sik , Lee Heung-Soo , Kim Kyung Sook , Eom Intae , Rah Seungyu
Published: August 2020

Resonant elastic x-ray scattering has been widely employed for exploring complex electronic ordering phenomena, such as charge, spin, and orbital order, in particular, in strongly correlated electronic systems. In addition, recent developments in pump–probe x-ray scattering allow us to expand the investigation of the temporal dynamics of such orders. Here, we introduce a new time-resolved Resonant Soft X-ray Scattering (tr-RSXS) endstation developed at the Pohang Accelerator Laboratory X-ray Free Electron Laser (PAL-XFEL). This endstation has an optical laser (wavelength of 800 nm plus harmonics) as the pump source. Based on the commissioning results, the tr-RSXS at PAL-XFEL can deliver a soft x-ray probe (400 eV–1300 eV) with a time resolution of ∼100 fs without jitter correction. As an example, the temporal dynamics of a charge density wave on a high-temperature cuprate superconductor is demonstrated.
Global stability of an adaptive immunity HIV dynamics model with silent and active cell-to-cell transmissions
Authors: Elaiw A. M. , AlShamrani N. H. , Hobiny A. D. , Abbas I. A.
Published: August 2020

This paper proposes and investigates an HIV dynamics model with adaptive immunity. The model describes the interactions between five compartments: healthy CD4+T cells, silent infected cells, active infected cells, free HIV particles, and cytotoxic T lymphocytes and antibodies. The model incorporates two methods of transmission: virus-to-cell and cell-to-cell (CTC). The healthy cells can be infected when they come into contact with free HIV particles or silent infected cells or active infected cells. We established that the model is well-posed by establishing the nonnegativity and boundedness of the solutions. The model has admitted five equilibria, and their existence is governed by five threshold parameters. We prove the global asymptotic stability of the equilibria by constructing Lyapunov functions. We have illustrated the theoretical results by numerical simulations. We have shown that the inclusion of CTC transmission decreases the concentration of healthy cells and increases the concentration of free HIV particles.
Granular superconductors for high kinetic inductance and low loss quantum devices
Authors: Glezer Moshe Aviv , Farber Eli , Deutscher Guy
Published: August 2020

Granular aluminum is a promising material for high kinetic inductance devices such as qubit circuits. It has the advantage over atomically disordered materials such as NbNx, to maintain a high kinetic inductance concomitantly with a high quality factor. We show that high quality nano-scale granular aluminum films having a sharp superconducting transition with normal state resistivity values on the order of 1×105 μΩ cm and kinetic inductance values on the order of 10 nH/◻ can be obtained, surpassing the state-of-the-art values. We argue that this is a result of the different nature of the metal-to-insulator transition, being electronic correlations driven (Mott type) in the former and disorder driven (Anderson type) in the latter.
Controlling the resistive switching hysteresis in VO2 thin films via application of pulsed voltage
Authors: Murtagh O. , Walls B. , Shvets I. V.
Published: August 2020

We investigate the origin of the variation in resistive switching hysteresis of VO2 thin films. Using pulsed electrical measurements in textured VO2 thin film devices, we show that the hysteresis observed in I–V curves results from Joule heating effects, particularly in the low-resistance state. The hysteresis is reduced by increasing the cooling time between pulses. Based on a mechanism of Joule heating-induced metal-insulator transition, numerical simulations are performed, which agree with the experimental variation in the hysteresis. Finally, a framework for engineering the I–V curves of VO2 devices is proposed.
Advanced field emission measurement techniques for research on modern cold cathode materials and their applications for transmission-type x-ray sources
Authors: Serbun P. , Porshyn V. , Müller G. , Lützenkirchen-Hecht D.
Published: August 2020

We report on the functional capabilities of our field emission (FE) measurement systems. The samples are prepared and inserted under clean room conditions and can be precisely xyz-positioned, heat-treated, and investigated in different vacuum environments and temperatures. The FE scanning microscope is a unique microscope being used for the localization of FE sites with high lateral resolution by means of extraction voltage U(x, y) or emission current I(x, y) maps over the cathode area of 25 × 25 mm2 and measuring the FE properties of localized emission sites or individual emitters. In contrast, the integral measurement system with the luminescent screen provides real-time integral information about the distribution of emission sites over the whole cathode during long- and short-term current stability measurements, thus allowing us to investigate the properties of various materials and their applications. Commissioning results with the upgraded systems using a silicon emitter array and a point-type graphene emitter will be given to demonstrate that both FE measurement techniques are very useful for an improved understanding and tailoring of materials for applications. The results showed that point-type graphene emitters are more preferable for practical applications. Using simulation software, a suitable triode configuration for point emitters was designed, and a current transmission ratio of ∼100% was obtained. The FE current stability of graphene emitters at pressures >10−3 Pa can be improved by heating the cathode at 100 °C–300 °C for 1 min–30 min. Finally, point-type graphene film emitters were used for transmission-type x-ray sources, and their applications in imaging and fluorescence spectroscopy are presented.
Numerical modeling of the distribution of virus carrying saliva droplets during sneeze and cough
Authors: Pendar Mohammad-Reza , Páscoa José Carlos
Published: August 2020

Violent respiratory diseases, i.e., coronavirus (COVID-19), spread through saliva in coughs and sneezes or are even exhaled in the form of microbial pathogen micro-droplets. Therefore, in this work, a comprehensive fully coupled Eulerian–Lagrangian method has been applied for infection control, thus leading to a deeper understanding of the saliva-disease-carrier droplet transmission mechanisms and also of their trajectory tracking by using the OpenFOAM package. This model determines the droplet–air interactions, the breakup process, and turbulent dispersion forces on each micro-droplet that is expelled within the respiratory tract in a correct way. By examining a broad range of initial velocities, size distributions, injection angles of saliva micro-droplets, and mouth opening areas, we predict the maximum opening area that can be driven by micro-droplets. One important contribution of this work is to present a correlation for the length and width of the overall direct maximum reach of the micro-droplets, driven by a wide range of mild coughs to intense sneezes. Our results indicate that the movement of the expelled droplets is mainly influenced by their size, angle, velocity, and environmental factors. During a virus crisis, like COVID-19, this paper can be used to determine the “social distance” between individuals to avoid contamination, by inhaling or touching their bodies, due to these saliva-disease-carrier droplets in sneezing, at various social distance positions such as face-to-face, meeting standing, and near equipment. The safe distance must be increased to around 4 m during a sneeze. By wearing a face mask and by bending the head during a sneeze as a protective action, we can reduce the contamination area to one-third and three-quarters, respectively. Furthermore, the dispersion of the film of the expelled saliva micro-droplets and the spatial relationship between the subjects, which affects the airflow inside the room, are also analyzed in detail.
3D micro fractal pipettes for capillary based robotic liquid handling
Authors: Decanini D. , Harouri A. , Mita Y. , Kim B. J. , Hwang G.
Published: August 2020

Miniaturized and mobile liquid handling devices are essential elements to biological or clinical applications. This will innovate the conventional liquid handling methods such as manual or automated pipetting systems. Here, we propose the micro fractal pipette as the candidate device for this objective. It is made of epoxy polymer and printed by innovative 3D nanoprinting technology based on two-photon absorption polymerization with sub-micrometer resolution. We demonstrated the efficient liquid handling performance by using the micro fractal pipette between the source droplet and the target hydrogel substrate. This is due to the high porosity (78%) and the 8.5 times larger cavity surface area compared to the full pyramid. The biomimetic inner cavity microchannel networks contribute to the low pressure drop. The proposed micro fractal pipette could also innovate the versatile and miniaturized liquid handling system, promising to various biological or clinical applications.
Dynamic orientation control of bimolecular electron transfer at charged micelle surfaces
Authors: Piechota Eric J. , Turro Claudia
Published: August 2020

Visible light excitation of the neutral complex [RuII(phen)2(bps)]0 (phen = 1,10-phenanthroline, bps = 4,7-biphenylsulfonate-1,10-phenanthroline) results in the formation of a triplet metal-to-ligand charge transfer excited state with a lifetime, τo, of 4.6 µs, where the promoted electron is localized on the bps ligand, 3*[RuIII(phen)2(bps•−)]0. The complex is dynamically quenched by di-n-heptyl-viologen, C7C7V2+, in solution and when the acceptor is embedded into negatively charged and neutral micelles. Addition of NaCl to solutions containing C7C7V2+ bound to negatively charged dodecyl sulfate sodium dodecyl sulfate micelles results in a monotonic increase in the quenching rate constant from kq = 6.0 × 107 to 1.7 × 109 M−1 s−1. In contrast, kq was independent of [NaCl] and diffusion limited in water and neutral micellar solution. Activated rate constants, kact, revealed that electron transfer was slowed by a factor of 450 when occurring in negatively charged micelle solution relative to neutral octaethylene glycol monododecyl ether (C12E8) micelles. In the 3*[RuIII(phen)2(bps•−)]0 excited state, the bps ligand is oriented away from the anionic micelle surface potential, −141 ≤ ψ ≤ −67 mV, due to a Frumkin effect operative in the deceleration of kact. Frumkin corrected rate constants were within a factor of three of those measured in C12E8 solution. Distance-dependent reorganization energies resulting from the orientation vary from 0.47 eV to 0.35 eV, while electronic coupling decreases by a factor of 10. The collective data show that orientation control over bimolecular rate constants in micellar solution can be achieved by screening micellar surface charges.
Frequency-dependent sensitivity of AC elastocaloric effect measurements explored through analytical and numerical models
Authors: Straquadine J. A. W. , Ikeda M. S. , Fisher I. R.
Published: August 2020

We present a comprehensive study of the frequency-dependent sensitivity for measurements of the AC elastocaloric effect by applying both exactly soluble models and numerical methods to the oscillating heat flow problem. These models reproduce the finer details of the thermal transfer functions observed in experiments, considering here representative data for single-crystal Ba(Fe1−xCox)2As2. Based on our results, we propose a set of practical guidelines for experimentalists using this technique. This work establishes a baseline against which the frequency response of the AC elastocaloric technique can be compared and provides intuitive explanations of the detailed structure observed in experiments.
Turbulent universality and the drift velocity at the interface between two homogeneous fluids
Authors: Samelson R. M.
Published: August 2020

The drift velocity U0 at the interface between two homogeneous turbulent fluids of arbitrary relative densities in differential mean motion is considered. It is shown that an analytical expression for U0 follows from the classical scaling for these flows when the scaling is supplemented by standard turbulent universality and symmetry assumptions. This predicted U0 is the weighted mean of the free-stream velocities in each fluid, where the weighting factors are the square roots of the densities of the two fluids, normalized by their sum. For fluids of nearly equal densities, this weighted mean reduces to the simple mean of the free-stream velocities. For fluids of two widely differing densities, such as air overlying water, the result gives U0 ≈ αV∞, where α ≪ 1 is the square root of the ratio of the fluid densities, V∞ is the free-stream velocity of the overlying fluid, and the denser fluid is assumed nearly stationary. Comparisons with two classical laboratory experiments for fluids in these two limits and with previous numerical simulations of flow near a gas–liquid interface provide specific illustrations of the result. Solutions of a classical analytical model formulated to reproduce the air–water laboratory flow reveal compensating departures from the universality prediction, of order 15% in α, including a correction that is logarithmic in the ratio of dimensionless air and water roughness lengths. Solutions reproducing the numerical simulations illustrate that the logarithmic correction can arise from asymmetry in the dimensionless laminar viscous sublayers.
The information catastrophe
Authors: Vopson Melvin M.
Published: August 2020

Currently, we produce ∼1021 digital bits of information annually on Earth. Assuming a 20% annual growth rate, we estimate that after ∼350 years from now, the number of bits produced will exceed the number of all atoms on Earth, ∼1050. After ∼300 years, the power required to sustain this digital production will exceed 18.5 × 1015 W, i.e., the total planetary power consumption today, and after ∼500 years from now, the digital content will account for more than half Earth’s mass, according to the mass-energy–information equivalence principle. Besides the existing global challenges such as climate, environment, population, food, health, energy, and security, our estimates point to another singular event for our planet, called information catastrophe.
Tailoring surface wettability to reduce chances of infection of COVID-19 by a respiratory droplet and to improve the effectiveness of personal protection equipment
Authors: Bhardwaj Rajneesh , Agrawal Amit
Published: August 2020

Motivated by the fact that the drying time of respiratory droplets is related to the spread of COVID-19 [R. Bhardwaj and A. Agrawal, “Likelihood of survival of coronavirus in a respiratory droplet deposited on a solid surface,” Phys. Fluids 32, 061704, (2020)], we analyze the drying time of droplets ejected from a COVID-19 infected subject on surfaces of personal protection equipment (PPE), such as a face mask, of different wettabilities. We report the ratio of drying time of the droplet on an ideal superhydrophobic surface (contact angle, θ → 180°) to an ideal hydrophilic surface (θ → 0°) and the ratio of the maximum to minimum drying time of the droplet on the surfaces with different contact angles. The drying time is found to be maximum if θ = 148°, while the aforementioned ratios are 4.6 and 4.8, respectively. These ratios are independent of the droplet initial volume, ambient temperature, relative humidity, and thermophysical properties of the droplet and water vapor. We briefly examine the change in drying time in the presence of impurities on the surface. Besides being of fundamental interest, the analysis provides insights that are useful while designing the PPE to tackle the present pandemic.
A predictive model of the temperature-dependent inactivation of coronaviruses
Authors: Yap Te Faye , Liu Zhen , Shveda Rachel A. , Preston Daniel J.
Published: August 2020

The COVID-19 pandemic has stressed healthcare systems and supply lines, forcing medical doctors to risk infection by decontaminating and reusing single-use personal protective equipment. The uncertain future of the pandemic is compounded by limited data on the ability of the responsible virus, SARS-CoV-2, to survive across various climates, preventing epidemiologists from accurately modeling its spread. However, a detailed thermodynamic analysis of experimental data on the inactivation of SARS-CoV-2 and related coronaviruses can enable a fundamental understanding of their thermal degradation that will help model the COVID-19 pandemic and mitigate future outbreaks. This work introduces a thermodynamic model that synthesizes existing data into an analytical framework built on first principles, including the rate law for a first-order reaction and the Arrhenius equation, to accurately predict the temperature-dependent inactivation of coronaviruses. The model provides much-needed thermal decontamination guidelines for personal protective equipment, including masks. For example, at 70 °C, a 3-log (99.9%) reduction in virus concentration can be achieved, on average, in 3 min (under the same conditions, a more conservative decontamination time of 39 min represents the upper limit of a 95% interval) and can be performed in most home ovens without reducing the efficacy of typical N95 masks as shown in recent experimental reports. This model will also allow for epidemiologists to incorporate the lifetime of SARS-CoV-2 as a continuous function of environmental temperature into models forecasting the spread of the pandemic across different climates and seasons.
A century of educational inequality in the United States
Authors: Jackson Michelle , Holzman Brian
Published: August 2020

Significance

There has been widespread concern that the takeoff in income inequality in recent decades has had harmful social consequences. We provide evidence on this concern by assembling all available nationally representative datasets on college enrollment and completion. This approach, which allows us to examine the relationship between income inequality and collegiate inequalities over the full century, reveals that the long-standing worry about income inequality is warranted. Inequalities in college enrollment and completion were low for cohorts born in the late 1950s and 1960s, when income inequality was low, and high for cohorts born in the late 1980s, when income inequality peaked. This grand U-turn means that contemporary birth cohorts are experiencing levels of collegiate inequality not seen for generations.
Neural transcription factor Pou4f1 promotes renal fibrosis via macrophage–myofibroblast transition
Authors: Tang Patrick Ming-Kuen , Zhang Ying-ying , Xiao Jun , Tang Philip Chiu-Tsun , Chung Jeff Yat-Fai , Li Jinhong , Xue Vivian Weiwen , Huang Xiao-Ru , Chong Charing Ching-Ning , Ng Chi-Fai , Lee Tin-Lap , To Ka-Fai , Nikolic-Paterson David J. , Lan Hui-Yao
Published: August 2020

Significance

Macrophage–myofibroblast transition (MMT) is a newly discovered pathogenic process by which TGF-β1/Smad3 signaling promotes tissue scarring. However, systemic targeting of Smad3 may impair host T cell immunity; therefore, it is preferable to focus on downstream mechanisms to identify antifibrotic therapies that avoid targeting Smad3 per se. In this study, we revealed a brain-specific transcription factor Pou4f1 as the key regulator by which TGF-β1/Smad3 signaling executes MMT. Macrophage-specific silencing of Pou4f1 effectively blocked progression of renal fibrosis in two mouse kidney disease models. Thus, Pou4f1 represents a therapeutic target in MMT-driven renal diseases.
Mismatch sensing by nucleofilament deciphers mechanism of RecA-mediated homologous recombination
Authors: Huang Xingyuan , Lu Ying , Wang Shuang , Sui Mingyu , Li Jinghua , Ma Jianbing , Ma Dongfei , Jia Qi , Hu Shuxin , Xu Chunhua , Li Ming
Published: August 2020

Significance

Homologous recombination (HR) is a major pathway for repair of double-stranded DNA break. The RecA proteins form a helical nucleofilament on single-stranded DNA (ssDNA) with a periodicity of ∼18 bases, which searches a donor DNA that is homologous to the ssDNA. The key point in HR is how the filament senses the sequence of the donor DNA. We designed a series of mismatch-containing donor DNAs to study HR and found that the strand exchange was blocked remotely by the mismatches. Our data suggest that the strand exchange progresses iteratively with the sequences being checked successively in ∼9-bp steps in the frontier of the extending synapsis, followed by a transitional segment that leads the post-strand-exchanged duplex.
Magnon Bose–Einstein condensation and superconductivity in a frustrated Kondo lattice
Authors: Volkov Pavel A. , Gazit Snir , Pixley Jedediah H.
Published: August 2020

Significance

Magnetically frustrated Kondo lattices are correlated metals not governed by symmetry-breaking quantum criticality, offering a new perspective on the puzzling phenomenology of strange metal behavior and unconventional superconductivity. While this concept is likely to be realized in certain heavy-fermion compounds, the corresponding models are notoriously difficult to solve, hindering robust theoretical predictions. Here we provide a comprehensive solution for a 1D Kondo ladder with a frustrated valence bond solid ground state in the presence of a magnetic field. We prove the stability of the field-induced magnon Bose–Einstein condensation and demonstrate the emergence of unconventional superconductivity. We also present strong evidence that our results carry over to two and three dimensions. These findings anchor future studies of frustrated heavy fermion systems.
Decreasing snow cover alters functional composition and diversity of Arctic tundra
Authors: Niittynen Pekka , Heikkinen Risto K. , Luoto Miska
Published: August 2020

Significance

Plant functional traits are central instruments in developing understanding and predicting biodiversity patterns and ecosystems processes. Snow is an important ecological factor in cold climates, but its contribution to the evolution of functionality of tundra vegetation is poorly known and insufficiently addressed in the research. We show here that snow has a fundamental effect in mediating climate change impacts on functional composition and diversity of Arctic tundra vegetation. As a whole, Arctic landscapes may lose spatial heterogeneity because plant communities will be functionally more alike, although the local functional diversity may increase. Our results highlight that future snow conditions and their fine-scale variability should be acknowledged in the next generation of Arctic vegetation−ecosystem models.
MicroRNA-dependent inhibition of PFN2 orchestrates ERK activation and pluripotent state transitions by regulating endocytosis
Authors: Sangokoya Carolyn , Blelloch Robert
Published: August 2020

Significance

The fibroblast growth factor–extracellular signal-regulated kinase (FGF-ERK) signaling pathway drives embryonic stem cells (ESCs) toward lineage commitment. How FGF-ERK signaling is regulated during this developmental window is poorly understood. Here we show that Profilin-2 (PFN2), an actin/dynamin-binding protein, controls FGF-ERK signaling in ESCs by regulating endocytosis. Members of the developmentally regulated miR-290 microRNA family suppress PFN2, enabling maximal FGF signaling, ESC proliferation, and ESC differentiation. These findings define a previously unknown axis of post-transcriptional control, endocytosis, and signal transduction important for ESC biology.
Mechanism of PRL2 phosphatase-mediated PTEN degradation and tumorigenesis
Authors: Li Qinglin , Bai Yunpeng , Lyle L. Tiffany , Yu Guimei , Amarasinghe Ovini , Nguele Meke Frederick , Carlock Colin , Zhang Zhong-Yin
Published: August 2020

Significance

The PRL phosphatases are highly oncogenic when overexpressed. However, the mechanism by which they promote tumorigenesis is unknown. Here, we reveal PTEN as a putative PRL2 substrate and define a mechanism for PTEN degradation through PRL2-mediated PTEN dephosphorylation. These insights immediately place the PRL2 phosphatase into the PI3K/AKT pathway, one of the critical signaling networks altered in cancer. We further demonstrate in a preclinical model that removal of
Prl2
in
Pten

+/−

mice increases the level of PTEN and inhibits PTEN heterozygosity-induced tumorigenesis. Given the observed inverse correlation between PRL2 expression and PTEN level, targeting PRL2 serves as a potential PTEN restoration strategy to treat cancers caused by PTEN deficiency.
Mucosal delivery of ESX-1–expressing BCG strains provides superior immunity against tuberculosis in murine type 2 diabetes
Authors: Sathkumara Harindra D. , Muruganandah Visai , Cooper Martha M. , Field Matt A. , Alim Md Abdul , Brosch Roland , Ketheesan Natkunam , Govan Brenda , Rush Catherine M. , Henning Lars , Kupz Andreas
Published: August 2020

Significance

Tuberculosis (TB) susceptibility and disease are significantly exacerbated in people with type 2 diabetes. The underlying mechanisms are incompletely understood, and it is not known if new TB vaccine candidates will be safe and provide protection in the context of diabetes. Using a long-term diet-induced murine model of type 2 diabetes, we demonstrate that increased susceptibility to TB is caused by impaired mycobacterial recognition and killing in the diabetic lung. Importantly, we show that mucosal vaccination of diabetic mice with Bacillus Calmette–Guérin (BCG) strains expressing the ESX-1 secretion system fromMycobacterium tuberculosiscan overcome this defect and provide superior immunity against TB. Our data warrant a consideration of ESX-1–containing BCG strains as effective TB vaccines in older individuals and diabetics.