bluuebunny/crossref_metadata_2025 huggingface dataset:
A one parameter damageable contact law for DEM, with application to frictional-cohesive granular materials
Authors: Couture Cyrille , Richefeu Vincent , Desrues Jacques , Bésuelle Pierre
Published: June 2021

A novel type of damageable cohesive law is presented for paired particle interactions in a DEM granular arrangement. It is designed in the spirit of a mixed breakage criterion for solid cohesion interaction, which can be implemented in parallel to a granular-frictional contact law. The evolution of damage at the contact level can be be easily modulated to enable a progressive transition from an initially linear elastic response to a loss of cohesion, by using a single parameterχ*. In a straightforward numerical implementation, the effect of this contact model is presented for a 3D periodic boundary condition DEM code. The results from a series of simulations show that, for a constant peak resistance of the cohesion, a more progressive damage result in an increase of the peak stress in a particle assembly, as well as a continuous transition in the stiffness of the stress-strain response around the peak stress.
Exploring the micromechanical behaviour of sand-rubber mixtures using X-ray micro-tomography
Authors: Cheng Zhuang , Wang Jianfeng , Li Wei
Published: June 2021

The micromechanical behaviour of sand-rubber mixtures (SRMs) under monotonic triaxial shear were investigated using X-ray micro-tomography. The localisation of sand particle rotations that occurred in a pure sand sample under shear was inhibited in the sand mixed with 30% rubber grains by mass. Meanwhile, the SRMs exhibited an evolution of sand-sand contact coordination number that is not negatively correlated with sample porosity, dramatically different from that was observed in pure sands. Substantially increasing anisotropy degree of sand-rubber contacts compared with minor changes of sandsand contact fabric was observed, implying the increasingly important role of sand-rubber contacts in the transmission of deviatoric loads as the shear of SRMs progressed.
Discrete modeling of waste rock dumps stability under seismic loading
Authors: Quezada Juan Carlos , Villavicencio Gabriel Eduardo
Published: June 2021

Copper mining produces significant amounts of associate waste, leading to the construction of huge mining waste dumps in the highly seismic zone of the Andes Mountains. To analyze the seismic stability of these deposits, it is necessary to characterize the mechanical properties of these materials in laboratory, which is quite difficult due to the large size of particles composing these structures. In this study, the global stability of mine waste dumps is analyzed by means of discrete element simulations. Three analogues upscaled particle size distributions were generated from the original PSD. The particles composing the dump were modeled using regular polygons. The modeled dumps were subject to a seismic loading by applying a velocity signal on the boundary walls, which was integrated directly from accelerometers database. The results show that failure in these structures is produced by infinite slope, for samples scaled by a factor until ten. This methodology is encouraging for the analysis of the global stability of mine waste dumps and for forecasting the runout distance after failure.
Modelling the monotonic and cyclic behaviour of sands using Artificial Neural Networks
Authors: Chen Weixian , Peña Olarte Andrés Alfonso , Cudmani Roberto
Published: June 2021

In this study artificial neural networks (ANN) are used to simulate the monotonic and cyclic behaviour of sands observed in laboratory tests on Karlsruhe sand under drained and undrained conditions. A genetic algorithm (GA) is used to obtain an optimal framework for the ANN. The results show that the proposed genetic adaptive neural network (GANN) can effectively simulate drained and undrained monotonic triaxial behaviour of saturated sand under isotropic or anisotropic consolidation. The GANN is also able to predict satisfactorily the cyclic behaviour of sands under undrained triaxial test with strain and stress cycles. In addition, GANN is able to distinguish between monotonic drained and undrained conditions by delivering a good prediction when trained with the combined database.
Optimal design of cyclones in series for the separation of multicomponent mixtures of Portland cement
Authors: Grave Juan C. , Paulo Cecilia I. , Petit Horacio. A. , Irassar E. Fabián
Published: June 2021

A nonlinear programming problem was developed for the separation and classification of Portland cement particles into different fractions through the optimal design of two cyclones classifier in series. The equations and restrictions considered included the global mass balances, the equations for the geometric design of the cyclones, the equations for the efficiency calculation, the operating limitations of the process and the pressure drops of the equipment. The results show that an increase on the particles cut size led to a greater dimensions cyclone, as expected. Moreover, fractional efficiencies obtained increase with the reduction of the cut size. The solids load effect is also evaluated, reductions of the solids feed by 50% of its maximum value does not result in a remarkably decrease of efficiencies values. The proposed model has provided useful information and constitutes a starting point for a better understanding of the overall separation process of multi-component Portland cement mixtures. It is a valuable tool for the correct design of this type of separators, given its versatility to optimize under different operating conditions and with different materials.
Seismic waves in the asteroid environment
Authors: Sánchez Paul , Scheeres Daniel J.
Published: June 2021

Through numerical simulations, we investigate impact generated seismic wave transmission in granular media under extremely low pressure. This mimics the conditions in the interior of asteroids and other small planetary bodies. We find a dependency not only on the overburden pressure on the medium, but also on the velocity of the impact that generates the wave. This is, at extremely low values of overburden pressure, the wave speed depends no only on the imposed pressure, but also on the increment in pressure created by the passing of the wave. We study crystalline and random packings and find very similar behaviour though with different wave speeds as expected. We then relate our results to different mission-related events on asteroids.
Mobilisation of friction in unstationary flows down a model topography
Authors: Blachier Baptiste , Staron Lydie
Published: June 2021

The frictional behaviour of a series of numerical 2D granular mass flows down a model topography is analysed. Effective friction coefficients estimated from final deposits are compared with data from documented natural geophysical flows, and show a consistent behaviour as far as run-out distances are concerned. The latter is used to estimate effective friction coefficients which capture well the frictional behaviour derived from the computation of micro-mechanical stress tensors near the gravity centre. Distinguishing between the different parts of the mass while spreading, we show that the downstream part of the flow exhibits a much larger friction than the core and the tail. A dependence between friction and flow volume is however observed in each region.
Particle velocity profile in an inclined rotating drum
Authors: Widhate P. , Zhu H. P. , Zeng Q. H. , Dong K. J.
Published: June 2021

Various experimental and numerical studies have been carried out to study the velocity profiles of the particles inside horizontal rotating drums, but little emphasis has been laid on inclined rotating drums, though these drums are extensively used in granular process industries. In this study, velocity profiles of the particles in a rotating drum with 0o, 5o, 10o, and 15o inclinations have been studied by using the discrete element method. It was found that at the locations of the drum with the volumetric fill in the range of 0.2 0.8, the inclined rotating drum has a similar variation of velocity with the radial height to the horizontal rotating drum. However, the variation of the average particle velocity along the length of the drum differs for horizontal and inclined drums. Furthermore, for the inclined rotating drum, the average velocity increases with the increase in the volumetric fill.
A procedure to join the force and volume ensemble statistical descriptions of granular media
Authors: Rey Juan Sebastián , Muñoz Jose Daniel , Oquendo William Fernando
Published: June 2021

Granular media consist of a large number of discrete particles interacting mostly through contact forces that, being dissipative, jeopardizes a classical statistical equilibrium approach based on energy. Instead, two independent equilibrium statistical descriptions have been proposed: the Volume Ensemble and the Force Network Ensemble. Hereby, we propose a procedure to join them into a single description, using Discrete Element simulations of a granular medium of monodisperse spheres in the limit state of isotropic compression as testing ground. By classifying grains according to the number of faces of the Voronoï cells around them, our analysis establishes an empirical relationship between that number of faces and the number of contacts on the grain. In addition, a linear relationship between the number of faces of each Voronoï cell and the number of elementary cells proposed by T. Aste and T. Di Matteo in 2007 is found. From those two relations, an expression for the total entropy (volumes plus forces) is written in terms of the contact number, an entropy that, when maximized, gives an equation of state connecting angoricity (the temperature-like variable for the force network ensemble) and compactivity (the temperature-like variable for the volume ensemble). So, the procedure establishes a microscopic connection between geometry and mechanics and, constitutes a further step towards building a complete statistical theory for granular media in equilibrium.
Non-equilibrium response and slow equilibration in hard disk systems
Authors: Mugita Daigo , Isobe Masaharu
Published: June 2021

The relaxation from a non-equilibrium state to the equilibrium depends on the methodologies and initial conditions. To investigate the microscopic mechanisms of equilibration systematically, we focus on the non-equilibrium response during the equilibration process induced by a disturbance of the homogeneous expansion of the simple hard disk systems. Large scale simulations by event-driven molecular dynamics revealed that an anomalous slow equilibration toward the liquid states emerges when starting from the co-existence phase. The origin of the slow decay mechanism is investigated using the probability distribution of local density and orientational order parameter.Their inhomogeneities seem to cause the anomalous slow equilibration.
LMGC90: a Contact Dynamics open source code for the simulation of granular asteroid with realistic regolith shapes. Application to the accretion process
Authors: Sánchez Paul , Renouf Mathieu , Azéma Emilien , Mozul Rémy
Published: June 2021

Granular asteroids are naturally occurring gravitational aggregates (rubble piles) bound together by gravitational forces. For this reason, it is reasonable to use the theoretical concepts and numerical tools developed for granular media to study them. In this paper, we extend the field of applicability of the Contact Dynamic (CD) method, a class of non smooth discrete element approach, for the simulation of three dimensional granular asteroids. The CD method is particularly relevant to address the study of dense granular assemblies of a large number of particles of complex shape and broad particles size distribution, since it does not introduces numerical artefacts due to contact stiffness. We describe how the open source software LMGC90, interfaced with an external library for the calculation of self-gravity, is used to model the accretion process of spherical and irregular polyhedral particles.
Avoiding chaos in granular dampers
Authors: Ferreyra María Victoria , Gómez-Paccapelo Julián M. , Suarez Ramiro , Pugnaloni Luis A.
Published: June 2021

Granular dampers are passive devices used to attenuate mechanical vibrations. The most common configuration consists in an enclosure, partiallyfilled with particles, attached to the vibrating structure that needs to be damped. The energy is dissipated due to inelastic collisions and friction between the grains and between the grains and the inner walls of the container as the structure vibrates. As a result of the collisions, the mechanical response of the system often results in chaotic motion even if the driving is harmonic. Despite the vibration attenuation achieved, this chaotic response may render the granular damper unsuitable for a range of applications. In this work, we showcase two simple modifications of the enclosure design that are able to mitigate the chaotic response of the granular damper. To this end we use Discrete Element Method simulations of: (a) a granular damper with a conical base, and (b) a granular damper with obstaclesfixed inside the enclosure. We compare results against a standardflat-base enclosure damper. The basic mechanical response of the dampers is characterized by measuring the apparent mass and the loss factor. The suppression of the chaotic response is assessed qualitatively via the phase space diagram.
A partial graphical model with a structural prior on the direct links between predictors and responses
Authors: Okome Obiang Eunice , Jézéquel Pascal , Proïa Frédéric
Published: June 2021

This paper is devoted to the estimation of a partial graphical model with a structural Bayesian penalization. Precisely, we are interested in the linear regression setting where the estimation is made through the direct links between potentially high-dimensional predictors and multiple responses, since it is known that Gaussian graphical models enable to exhibit direct links only, whereas coefficients in linear regressions contain both direct and indirect relations (due e.g. to strong correlations among the variables). A smooth penalty reflecting a generalized Gaussian Bayesian prior on the covariates is added, either enforcing patterns (like row structures) in the direct links or regulating the joint influence of predictors. We give a theoretical guarantee for our method, taking the form of an upper bound on the estimation error arising with high probability, provided that the model is suitably regularized. Empirical studies on synthetic data and a real dataset are conducted.
Individual Muscle Adaptations in different Resistance Training Systems in Well-Trained Men
Authors: Angleri Vitor , Ugrinowitsch Carlos , Libardi Cleiton Augusto
Published: June 2021

Using a within-subject design we compared the individual responses between drop-set (DS) vs. traditional resistance training (TRAD) (n=16) and crescent pyramid (CP) vs. TRAD (n=15). Muscle cross-sectional area (CSA), leg press and leg extension 1 repetition maximum (1-RM) were assessed pre and post training. At group level, CSA increased from pre to post (DS: 7.8% vs. TRAD: 7.5%, P=0.02; CP: 7.5% vs. TRAD: 7.8%, P=0.02). All protocols increased the 1-RM from pre to post for leg press (DS: 24.9% vs. TRAD: 26.8%, P < 0.0001; CP: 27.3% vs. TRAD:2 6.3%, P < 0.0001) and leg extension (DS: 17.1% vs. TRAD: 17.3%, P < 0.0001; CP: 17.0% vs. TRAD: 16.6%, P < 0.0001). Individual analysis for CSA demonstrated no differences between protocols in 15 subjects. For leg press 1-RM, 5 subjects responded more to TRAD, 2 to DS and 9 similarly between protocols. In TRAD vs. CP, 4 subjects responded more to CP, 1 to TRAD and 10 similarly between protocols. For leg extension 1-RM 2 subjects responded more to DS, 3 to TRAD and 11 similarly between protocols. Additionally, 2 subjects responded more to CP, 2 to TRAD and 11 similarly between protocols. In conclusion, all protocols induced similar individual responses for CSA. For 1-RM, some subjects experience greater gains for the protocol performed with higher loads, such as CP.
Ruthenium-Catalyzed Asymmetric Dehydrative Allylic Cyclization of Five-Membered Chalcogen Heteroaromatics
Authors: Tanaka Shinji , Kitamura Masato , Iwase Shoutaro , Kanda Sena , Kato Marie , Kiriyama Yutaro
Published: June 2021

The asymmetric dehydrative intramolecular allylation reactions of furan and thiophene were performed using a cationic cyclopentadienyl-ruthenium (CpRu) complex of a chiral pyridine carboxylic acid, namely Cl-Naph-PyCOOH. Both furan and thiophene tethered with an allylic alcohol gave the corresponding bicyclic compounds in high yields and enantioselectivities using 0.1–5 mol% of the catalyst. The reaction was found to proceed via a similar enantioface selection mechanism to that previously reported by our group, which involved halogen and hydrogen bond formation, in addition to the generation of an intermediate σ-allyl complex.
Ocular Trauma with Ophthalmic Artery Injury as a Rare Cause of Subarachnoid Hemorrhage: a Case Report and Review of the Literature
Authors: Veldeman Michael , Ridwan Hani , Hasan Dimah , Rieg Annette , Clusmann Hans , Schubert Gerrit Alexander
Published: June 2021

Background and Importance Traumatic avulsion of the ophthalmic artery is a rare cause of subarachnoid hemorrhage (SAH). In this case, a relative minor fall with isolated ocular trauma caused bulbar dislocation and rupture of the ophthalmic artery in its intracranial segment resulting in subarachnoid bleeding.

Clinical Presentation In a female patient in her 70s, a direct penetrating trauma to the orbit by a door handle resulted in basal SAH with blood dispersion into both Sylvian fissures. Cerebral angiography revealed a blunt-ending stump at the origin of the ophthalmic artery. To provide protection against further bleeding, a flow diverter stent was placed in the internal carotid artery to cover the origin of the ophthalmic artery. After a longer intensive care stay complicated by pneumonia and respiratory insufficiency, the patient made a full recovery. Of all four reported cases (including ours), delayed cerebral ischemia was seen in one patient and hydrocephalus in two patients. These potential complications necessitate close observation and fitting treatment similar to aneurysmal SAH.

Conclusion Due to similar physiologic aspects, this type of bleed mimics many aspects of aneurysmal SAH. In this case, we observed no hydrocephalus or the development of delayed cerebral ischemia. This represents, however, the first reported case treated by placement of a flow diverter stent to prevent rebleeding and pseudoaneurysm formation.
Inhibitory Effects of Alendronate on Adhesion and Viability of Preosteoblast Cells on Titanium Discs
Authors: Lilakhunakon Charukrit , Suwanpateeb Jintamai , Patntirapong Somying
Published: June 2021

Objective This study aimed to investigate the effects of alendronate (ALN; a bisphosphonate) on adhesion and viability of preosteoblasts using different cell passages on sandblasted and acid-etched (SLA) Ti surfaces.

Materials and Methods Preosteoblast, MC3T3, cells (passage 42; P42 and passage 62; P62) were cultured with ALN (1 and 5 µM) on cell culture plate for 7 days. Cells were lifted, counted, and seeded on SLA Ti surfaces. Cells were incubated on the discs for 6 hours to examine cell adhesion by using confocal microscopy and for 24 hours to determine cell viability by using MTT assay.

Results ALN interfered with cell adhesion on Ti surfaces by reducing the cell number in both cell passages. Nuclei of untreated cells showed oval shape, whereas some nuclei of ALN-treated cells demonstrated crescent and condensed appearance. ALN at 1 and 5 µM significantly decreased nuclear area and perimeter in P42, while ALN at 5 µM reduced nuclear area and perimeter in P62. After 24 hours, cells (P42) grown on Ti surfaces showed decreased cell viability when culturing with 5 µM ALN.

Conclusion ALN reduced cell adhesion and viability of preosteoblasts on Ti surfaces. ALN treatment seemed to exert higher inhibitory effects on nuclear shape and size as well as cell viability in lower cell passage. This led to the reduction in cell to implant surface interaction after encountering bisphosphonate treatment.
The Effects of Vasonatrin Peptide on Fat Graft Viability: An Experimental Study
Authors: Irmak Fatih , Sizmaz Mert , Sirvan Selami Serhat , Karsidag Semra , Ozagari Aysim
Published: June 2021

Vasonatrin peptide (VNP) is a synthetic peptide that possesses vasodilatory, natriuretic, and anti-inflammatory properties. The authors aimed to analyze the effects of VNP on fat graft survival. Twenty Sprague–Dawley rats are randomly divided into two groups of 10. Fat grafts are harvested from the right inguinal region. After preparation, fat grafts are placed to the interscapular region. The first group of rats were administered VNP after their fat injection, while the second group received tail-vein injections of an equal volume of sterile saline following their fat injection. Experiment and control groups are evaluated according to their level of degeneration of adipocytes, fat necrosis, vacuolization, cyst formation in adipocytes, fibrosis of the fat tissue, capillary density, and CD31 immunohistochemical staining. Degeneration, vacuolization, and cyst formation in adipocytes were lower in the experiment group. Increased capillary density in the experiment group was demonstrated by CD31 antibody staining and by counting capillary density under a microscope. The average percentage of change in weight of the fat grafts in the experiment group was lower than that in the control group. The results indicate that VNP has some beneficial effects on fat graft survival by multiple independent mechanisms that influence both local and systemic homeostasis.
Existence of an energy function for three-dimensional chaotic “sink-source” cascades
Authors: Barinova M. , Grines V. , Pochinka O. , Yu B.
Published: June 2021

This paper is a continuation of research in the direction of energy function (a smooth Lyapunov function whose set of critical points coincides with the chain recurrent set of a system) construction for discrete dynamical systems. The authors established the existence of an energy function for any A-diffeomorphism of a three-dimensional closed orientable manifold whose non-wandering set consists of a chaotic one-dimensional canonically embedded surface attractor and repeller.
Comment on “A study on improvement of discharge characteristic by using a transformer in a capacitively coupled plasma” [Phys. Plasmas 22, 123504 (2015)]
Authors: Ding Z. F.
Published: June 2021

In the paper [Y.C. Kim et al., Phys. Plasmas 22, 123504 (2015)], the plasma density in radio frequency (RF) capacitively coupled plasma was increased by introducing a step-down ferrite-core transformer into a conventional type-T impedance matching network. The authors ascribed the increment in plasma density to the reduction of DC self-bias. Although this correlation was roughly right, but behaviors of the DC self-bias in the asymmetric RF discharge that was non-linearly interacted with the external circuit were not discussed. In practical applications, this approach of increasing plasma density will be limited by the rapid increase in power loss in step-down ferrite-core transformer operating in high-power 13.56 MHz discharges and the still high DC self-bias governed by the asymmetric geometry.
On the possibility of creating a magnetic field with a given degree of spatial inhomogeneity
Authors: Fishbein L. A.
Published: June 2021

Proposed here is a method for constructing systems of circular thin Helmholtz coils (conic coils), which makes it possible to obtain a magnetic field with any degree of inhomogeneity by doubling the number of coils. A functional relationship is obtained between the currents of the coils and their distances to the center, which allows zeroing all derivatives in the expansion of the magnetic field in a series in spatial variables in the center of the system to a derivative of arbitrary order. An analytical expression is obtained for the magnitude of the magnetic field of the systems along the axis of symmetry. All the systems considered here have the same parity (oddness) of the projections of the magnetic field with respect to spatial variables and equal inhomogeneity in all directions in the center of symmetry.
Quantum analysis on the convergence speed of exponential product formulas — differential-subtraction and exchange-integration method on concise norm bounds
Authors: Suzuki Masuo
Published: June 2021

A general method to evaluate rigorously concise norm bounds on the difference between the original exponential operators and their corresponding exponential product formulas is proposed, in order to evaluate the convergence speed of exponential product formulas for a new kind of exponential operator, exp(x2[A, B]). One of the remarkable results on this issue is given by the following formula: e[A,B] is equal to the n → ∞ limit of the product (exp(iA/n)exp(−iB/n)exp(−iA/n)exp(iB/n))n2 for the Hermitian operators A and B. The convergence speed of this formula is proved rigorously to be O(1/n) even for unbounded operators A and B under the condition that the third-order free Lie elements of A and B should be bounded in norm.
Visualization of transformation toughening of zirconia ceramics during dynamic fracture
Authors: Takagi Sota , Inukai Koji , Kawai Nobuaki , Nozawa Shunsuke , Kyono Atsushi , Fukaya Ryo , Adachi Shin-ichi , Ichiyanagi Kouhei
Published: June 2021

Establishing a mechanistic understanding of dynamic fracture is critical for the design of efficient and safe structural materials. Transformation toughening describes the process by which a crystal structure change can reduce the crack-driving force. The understanding of the dynamic behavior of transformation-toughened materials is limited. To clarify the relationship between crystal structure transformations and toughening during a dynamic loading, we carried out a time-resolved x-ray diffraction study of yttria-stabilized tetragonal zirconia polycrystal under shock loading. The results show that the ambient tetragonal crystal structure is maintained on loading and phase transformation to the monoclinic phase occurs only after the onset of dynamic fracture, indicating that the transformation toughening is associated with dynamic fracture caused by wave interactions. This study not only revealed the reason for the high spall strength of zirconia ceramics but also demonstrated the great potential for time-resolved x-ray diffraction method to study fracture dynamics.
A study of the foil explosion in vacuum using spectral streak camera diagnostics
Authors: Baksht R. B. , Tkachenko S. I. , Zhigalin A. S. , Rousskikh A. G. , Oreshkin V. I.
Published: June 2021

The foil explosion in vacuum was studied experimentally using a spectral streak camera. The experiment was performed with Cu, Al, Ni, and Ti foils of thickness 6 μm at a current density rise rate of ∼6 × 105 A/(cm2 ns). For all exploded foils, a plasma corona was formed in the gas desorbed from the foil surface when the voltage across the discharge gap reached the collapse voltage. In the Cu, Al, and Ni foil explosions, the specific deposited energy εdep was sufficient for complete melting but insufficient for vaporization of the foil material. However, the streaked spectra obtained for these foil explosions contained the foil material lines that appeared 80–200 ns after tcoll. The authors hypothesize that these lines appeared as a result of the decaying of the metastable liquid state of the exploded foil metal, which took place at a certain time after the core was shunted. In the Ti foil explosion, the deposited energy was insufficient to melt the metal, the transition to the metastable liquid state did not occur, and the discharge plasma spectrum did not contain lines of the foil material.
Superior ionic conduction in LiAlO2 thin-film enabled by triply coordinated nitrogen
Authors: Guan Min , Huang Kai , Mou Suwei , Jiang Chunzhi , Pang Yuncong , Xiang Andrew , Chen Jun Song , Xiang Yong , Zhang Xiaokun
Published: June 2021

Developing a highly Li+-conductive thin-film electrolyte remains a challenge for the application of all-solid-state thin-film batteries. This paper reports an N-doped LiAlO2 glassy thin-film with high ionic conductivities prepared by reactive sputtering under an N2 atmosphere after the pattern of the gold standard LiPON thin-film solid electrolyte. The resulting Li+-conductive thin-film is dense without cracks and shows good adhesion to substrates. The doped N partially substitutes O and yields a triple coordination structure in the thin-films, which leads to an enhancement of ionic conductivity up to 3 orders of magnitude compared to pristine LiAlO2. On one hand, the triply coordinated nitrogen facilitates the formation of a cross-linked network and provides continuous pathways for Li+ transport. On the other hand, the triply coordinated nitrogen could provide additional hopping sites for Li+, which have a relatively weak bonding force to Li+ than O. This gives rise to an N-doped LiAlO2 thin-film with an ionic conductivity of 3.99 × 10−6 S/cm at room temperature. To the best of our knowledge, this is one of the highest ionic conductivities ever reported for LiPON-like thin-film solid electrolytes.
Evolution of instability modes in Mach 10 frozen and chemically reacting boundary layers by means of non-linear parabolized stability equations
Authors: Zanus L. , Pinna F.
Published: June 2021

The physical mechanisms and laminar-to-turbulent transition scenarios characterizing hypersonic flows are not yet completely identified and well described as in low-supersonic and subsonic regimes. Particularly, there is a lack of knowledge about the role chemistry plays and the effects that high temperature has on the transition non-linear stages. In this study, transition in a Mach 10 adiabatic flat-plate boundary layer is investigated by means of non-linear parabolized stability equations, considering both frozen and chemical non-equilibrium (CNE) flow assumptions. A tendency to switch from a H- to a K-type transition scenario at the increment of the primary-mode initial amplitude is found, similar to what occurs in subsonic and low-supersonic regimes. Secondary-waves' initial amplitudes do not affect directly the occurring breakdown type, but they significantly influence the evolution of the higher harmonics, in particular the generation of streamwise steady vortices. Chemical reactions play an indirect role in transition through the determination of the laminar base flow and the linear stability characteristics of the primary instability. Excitation of secondary modes is weaker in CNE than in frozen conditions, but qualitatively similar. Contrary to previous studies, assuming frozen perturbations in a chemically reacting base flow is found to have a significant effect on the higher-harmonics amplitudes, in particular on the relative evolution of the secondary modes.
Optimization of selective two-photon absorption in cavity polaritons
Authors: Carnio Edoardo G. , Buchleitner Andreas , Schlawin Frank
Published: June 2021

We investigate optimal states of photon pairs to excite a target transition in a multilevel quantum system. With the help of coherent control theory for two-photon absorption with quantum light, we infer the maximal population achievable by optimal entangled vs separable states of light. Interference between excitation pathways as well as the presence of nearby states may hamper the selective excitation of a particular target state, but we show that quantum correlations can help to overcome this problem and enhance the achievable “selectivity” between two energy levels, i.e., the relative difference in population transferred into each of them. We find that the added value of optimal entangled states of light increases with broadening linewidths of the target states.
ordpy: A Python package for data analysis with permutation entropy and ordinal network methods
Authors: Pessa Arthur A. B. , Ribeiro Haroldo V.
Published: June 2021

Since Bandt and Pompe’s seminal work, permutation entropy has been used in several applications and is now an essential tool for time series analysis. Beyond becoming a popular and successful technique, permutation entropy inspired a framework for mapping time series into symbolic sequences that triggered the development of many other tools, including an approach for creating networks from time series known as ordinal networks. Despite increasing popularity, the computational development of these methods is fragmented, and there were still no efforts focusing on creating a unified software package. Here, we present ordpy (http://github.com/arthurpessa/ordpy), a simple and open-source Python module that implements permutation entropy and several of the principal methods related to Bandt and Pompe’s framework to analyze time series and two-dimensional data. In particular, ordpy implements permutation entropy, Tsallis and Rényi permutation entropies, complexity–entropy plane, complexity–entropy curves, missing ordinal patterns, ordinal networks, and missing ordinal transitions for one-dimensional (time series) and two-dimensional (images) data as well as their multiscale generalizations. We review some theoretical aspects of these tools and illustrate the use of ordpy by replicating several literature results.
Analysis of energy transfer through direct numerical simulations of magnetohydrodynamic Orszag–Tang vortex
Authors: Jadhav Kiran , Chandy Abhilash J.
Published: June 2021

Direct numerical simulations of magnetohydrodynamic turbulence with Orszag–Tang vortex initial conditions are presented here for two different Reynolds numbers. Simulations of this transition-to-turbulence problem are carried out using a pseudo-spectral code with a grid resolution fine enough to resolve the Kolmogorov scale. The power-law behavior of bulk quantities like kinetic energy, magnetic energy, integral length scales, and enstrophy is analyzed. For a low Reynolds number, weak turbulence spectra are observed with a slope of −2.0 in the inertial subrange, while for a higher Reynolds number, the spectra exhibit a slope very close to the Kolmogorov spectra of −5/3. The Q-criteria isosurfaces at the time instant of maximum enstrophy are used for the visualization of turbulence developed within the flow. Furthermore, a new approach is presented to understand the dynamics of the transfer between kinetic and magnetic energies in the early period of development using the energy flux spectra, rate of change of kinetic and magnetic energies, and current density structures, which employ a three-dimensional representation of the alignment between velocity and magnetic field across the structures.
Microstructure and heteroatom dictate the doping mechanism and thermoelectric properties of poly(alkyl-chalcogenophenes)
Authors: Gordon Madeleine P. , Gregory Shawn A. , Wooding Jamie P. , Ye Shuyang , Su Gregory M. , Seferos Dwight S. , Losego Mark D. , Urban Jeffrey J. , Yee Shannon K. , Menon Akanksha K.
Published: June 2021

Heteroatom substitution can favorably alter electronic transport in conductive polymers to improve their thermoelectric performance. This study reports the spectroscopic, structural, and thermoelectric properties of poly(3–(3′,7′-dimethyloctyl) chalcogenophenes) or P3RX doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), where the heteroatom [X = thiophene (T), selenophene (Se), tellurophene (Te)], the doping methodology, and extent of doping are systematically varied. Spectroscopic measurements reveal that while all P3RX polymers are appreciably doped, the doping mechanism is inherently different. Poly(3-hexylthiophene) (P3HT, used as a control) and poly(3–(3′,7′-dimethyloctyl)tellurophene) (P3RTe) are doped primarily via integer charge transfer (ICT), whereas poly(3–(3′,7′-dimethyloctyl)selenophene) (P3RSe) and poly(3–(3′,7′-dimethyloctyl)thiophene) (P3RT) are doped via charge transfer complex (CTC) mechanisms. Despite these differences, all polymers saturate with roughly the same number of F4TCNQ counterions (1 dopant per 4 to 6 heterocycles), reinforcing the idea that the extent of charge transfer varies with the doping mechanism. Grazing incidence wide-angle x-ray scattering measurements provide insight into the structural driving forces behind different doping mechanisms—P3RT and P3RSe have similar microstructures in which F4TCNQ intercalates between the π-stacked backbones resulting in CTC doping (localized carriers), while P3HT and P3RTe have microstructures in which F4TCNQ intercalates in the alkyl side chain region, giving rise to ICT doping (delocalized carriers). These structural and spectroscopic observations shed light on why P3HT and P3RTe obtain electrical conductivities ca. 3 S/cm, while P3RT and P3RSe have conductivities <10−3 S/cm under the same thin film processing conditions. Ultimately, this work quantifies the effects of heteroatom, microstructural ordering, extent of doping, and doping mechanism, thereby providing rational guidance for designing future thermoelectric polymer-dopant systems.
Influence of finite ion size and dielectric decrement on the ion current rectification in a single conical nanopore
Authors: Pandey Doyel , Bhattacharyya Somnath
Published: June 2021

The ion current rectification (ICR) arising due to the transport of ionized liquids within a geometrically asymmetric nanopore is of great significance for the development of smart nanogadgets with unique working capabilities. Though the theoretical framework for the ICR is well developed, the influence of the finite size of ions on the ICR phenomena had not been addressed before. The ion steric repulsion due to finite ion size and dielectric decrement of the medium creates a counterion saturation. In this study, a modified electrokinetic model is adopted to describe the ICR phenomena of a single conical nanopore by considering the hydrated ions as finite-sized dielectric charged spheres. The Nernst–Planck equations for ion transport are modified to incorporate the short-range ion steric interactions modeled by the Boublik–Mansoori–Carnahan–Starling–Leland equation as well as Born force and dielectrophoretic force acting on the hydrated ions engender by the ion–solvent interactions. The counterion saturation attenuates the shielding effect of the surface charge of the nanopore leading to a larger ζ-potential and hence, a larger volume flux and reduced conduction. We find that the ion steric interactions and the dielectric decrement significantly influence the ICR phenomena as well as the ion selectivity of a conical nanopore, especially for moderate to high range of surface charge density, bulk concentration, and applied bias. We find that ICR varies linearly with temperature; however, the variation is found to be marginal. Our results show that the volume flux and the rectification factor of the conical nanopore can be suitably tuned by adding salt of larger counterion size or multivalent ions.
Switchable photovoltaic response in hexagonal LuMnO3 single crystals
Authors: Sheng Yunwei , Fina Ignasi , Gospodinov Marin , Fontcuberta Josep
Published: June 2021

Hexagonal manganites, such as h-LuMnO3, are ferroelectric with its polar axis along the hexagonal axis and have a narrow electronic bandgap (≈1.5 eV). Using Pt electrodes, h-LuMnO3 single crystals display a strong rectification, characteristic of a Schottky diode, and a large photoresponse. It is found that the short circuit photocurrent density Jsc along the polar axis is modulated (up to 25%) by the direction of the ferroelectric polarization P, leading to a short circuit photocurrent loop that mimics the ferroelectric polarization. However, a non-switchable Jsc persists. Diffusion photocurrent is shown to dominate current-in-plane measurements and contributes to the non-switchable Jsc. This observation illustrates the dramatic role of the large optical absorption in hexagonal manganites. The accompanying optical dichroism might challenge disentangling a genuine bulk photovoltaic response in h-LuMnO3 single crystals, contributing to the non-switchable Jsc. Epitaxial thin films may offer a suitable alternative.
Geometric unfolding of synchronization dynamics on networks
Authors: Arola-Fernández Lluís , Skardal Per Sebastian , Arenas Alex
Published: June 2021

We study the synchronized state in a population of network-coupled, heterogeneous oscillators. In particular, we show that the steady-state solution of the linearized dynamics may be written as a geometric series whose subsequent terms represent different spatial scales of the network. Specifically, each additional term incorporates contributions from wider network neighborhoods. We prove that this geometric expansion converges for arbitrary frequency distributions and for both undirected and directed networks provided that the adjacency matrix is primitive. We also show that the error in the truncated series grows geometrically with the second largest eigenvalue of the normalized adjacency matrix, analogously to the rate of convergence to the stationary distribution of a random walk. Last, we derive a local approximation for the synchronized state by truncating the spatial series, at the first neighborhood term, to illustrate the practical advantages of our approach.
Local and network behavior of bistable vibrational energy harvesters considering periodic and quasiperiodic excitations
Authors: Rajagopal Karthikeyan , Ramesh Arthanari , Moroz Irene , Duraisamy Prakash , Karthikeyan Anitha
Published: June 2021

Vibrational energy harvesters can exhibit complex nonlinear behavior when exposed to external excitations. Depending on the number of stable equilibriums, the energy harvesters are defined and analyzed. In this work, we focus on the bistable energy harvester with two energy wells. Though there have been earlier discussions on such harvesters, all these works focus on periodic excitations. Hence, we are focusing our analysis on both periodic and quasiperiodic forced bistable energy harvesters. Various dynamical properties are explored, and the bifurcation plots of the periodically excited harvester show coexisting hidden attractors. To investigate the collective behavior of the harvesters, we mathematically constructed a two-dimensional lattice array of the harvesters. A non-local coupling is considered, and we could show the emergence of chimeras in the network. As discussed in the literature, energy harvesters are efficient if the chaotic regimes can be suppressed and hence we focus our discussion toward synchronizing the nodes in the network when they are not in their chaotic regimes. We could successfully define the conditions to achieve complete synchronization in both periodic and quasiperiodically excited harvesters.
Domain structure evolution during alternating current poling and its influence on the piezoelectric properties in [001]-cut rhombohedral PIN-PMN-PT single crystals
Authors: Ushakov A. D. , Hu Q. , Liu X. , Xu Z. , Wei X. , Shur V. Ya.
Published: June 2021

Extensively studied PMN-PT and PIN-PMN-PT crystals with compositions close to the morphotropic phase boundary possess excellent piezoelectric characteristics. Recently developed alternating current treatment enhances the piezoelectric performance even further. Here, we demonstrate the results of studying the domain structure evolution by direct optical imaging during polarization reversal in [001]-oriented PIN-PMN-PT single crystals of rhombohedral phase during alternating current poling (ACP). The main types of domain structures involved in polarization reversal were revealed. Cross-like domain structure (CDS) was found to be undesirable for the piezoelectric application. The ACP-treatment proved to be effective in reducing the CDS fraction as a result of the growth of lens-shaped domains attributed to the 71° switching. The interaction of cross-like and lens-shaped domains was proposed as a key mechanism for improving the piezoelectric properties by the ACP-treatment. Comparison of the switching current with optical images revealed the correlation between the CDS area and electric field corresponding to the current maximum. This fact allows optimizing the number of the ACP-treatment pulses based on the switching current data without optical imaging.
Inactivation of common airborne antigens by perfluoroalkyl chemicals modulates early life allergic asthma
Authors: Wang Mengjing , Li Qianqian , Hou Meifang , Chan Louisa L. Y. , Liu Meng , Ter Soo Kai , Dong Ting , Xia Yun , Chotirmall Sanjay H. , Fang Mingliang
Published: June 2021

Significance

Perfluoroalkyl chemicals (PFCs) are man-made chemicals ubiquitously present in humans. We demonstrate that a major PFC, perfluorooctane sulfonate (PFOS), dampens mice from developing house dust mite (HDM)–induced asthma, while abolishing the microbial product LPS’s protective effect in asthma development. This finding has direct human relevance, considering the low-PFOS concentrations necessary for its effect. Mechanistically, PFOS binds with high affinity to Der p1, a major allergen from HDM, as well as to the lipid A moiety of LPS, resulting in their inactivation. Our data highlight that PFC exposure may play a previously unappreciated role in modulating allergic asthma and emphasize the importance of reducing exposure.
The impact of a lack of mathematical education on brain development and future attainment
Authors: Zacharopoulos George , Sella Francesco , Cohen Kadosh Roi
Published: June 2021

Significance

Our knowledge of the effect of a specific lack of education on the brain and cognitive development is currently poor but is highly relevant given differences between countries in their educational curricula and the differences in opportunities to access education. We show that within the same society, adolescent students who specifically lack mathematical education exhibited reduced brain inhibition levels in a key brain area involved in reasoning and cognitive learning. Importantly, these brain inhibition levels predicted mathematical attainment ∼19 mo later, suggesting they play a role in neuroplasticity. Our study provides biological understanding of the impact of the lack of mathematical education on the developing brain and the mutual play between biology and education.
Homocysteine fibrillar assemblies display cross-talk with Alzheimer’s disease β-amyloid polypeptide
Authors: Sade Yazdi Dorin , Laor Bar-Yosef Dana , Adsi Hanaa , Kreiser Topaz , Sigal Shahaf , Bera Santu , Zaguri Dor , Shaham-Niv Shira , Oluwatoba Damilola S. , Levy Davide , Gartner Myra , Do Thanh D. , Frenkel Dan , Gazit Ehud
Published: June 2021

Significance

The accumulation of homocysteine, a key metabolite, is considered a risk factor for Alzheimer’s disease. This work demonstrates the ability of homocysteine to form ordered fibrillar structures. The toxicity of these structures is demonstrated in a yeast model that accumulates homocysteine. We further show the association of this observation with Alzheimer's disease pathology, including induced aggregation of a pathological protein and the presence of homocysteine structures in the brain of model mice. We suggest the targeting of homocysteine structure formation as a direction for Alzheimer's disease therapeutics.
Targeting the tetraspanin CD81 reduces cancer invasion and metastasis
Authors: Vences-Catalán Felipe , Rajapaksa Ranjani , Kuo Chiung-Chi , Miller Caitlyn L. , Lee Anderson , Ramani Vishnu C. , Jeffrey Stefanie S. , Levy Ronald , Levy Shoshana
Published: June 2021

Significance

CD81 belongs to the evolutionary conserved tetraspanin family of proteins that form specialized membranal platforms that facilitate a vast array of cellular processes. However, little is known about the consequences of these molecular interactions under normal or pathological conditions. Tetraspanins have no known natural ligands, but ligation by some antibodies induces functional consequences. Here we show that engagement of CD81 with 5A6 halts tumor invasion in vitro and reduces breast cancer metastasis in vivo. Altogether, these finding highlight the role of CD81 in cancer progression.