bluuebunny/crossref_metadata_2025 huggingface dataset:
The evidence ecosystem in South Africa: growing resilience and institutionalisation of evidence use
Authors: Stewart Ruth , Dayal Harsha , Langer Laurenz , van Rooyen Carina
Published: August 2019

The evidence-informed approach to policy-making and implementation is, at its core, about better decisions for a better future. It is focused on the effective use of scarce resources, on avoiding harm and maximising good. It is grounded in principles of equity and equality, of accountability and transparency. Given these characteristics, for those of us who work in this field, there is arguably a moral, economic, social and political case for paying closer attention to evidence-informed decision-making ecosystems in the South. Evidence-based policy and implementation, or evidence-informed decision-making in line with the most recent thinking, is often framed from two inter-related but limited perspectives: first, it is viewed as an approach that has originated from ‘developed’ Northern countries, and second, it is conceptualised as a technical intervention. However, there has been a shift in how the approach is conceived, moving away from assumptions that it is an intervention implemented from outside, from the North, for the benefit of the South. As part of this shift, certain initiatives in Africa have gained greater momentum. It is in acknowledging that there are different ways to think (epistemic diversity) about Southern evidence-informed decision-making, that this work has arisen. It seizes on the opportunity to view evidence-informed decision-making in a new light, exploring the evidence ecosystems in the South as systems strongly influenced by, but not defined by, Northern stimuli, including, but not limited to, technical interventions. This work set out to describe the evidence ecosystem in South Africa. In doing so, it finds that the ecosystem is increasingly resilient despite some limitations. It has strong structural foundations, includes many diverse organisations, is supported by not inconsiderable investment, is enabled by growing and significant capacity, contains iterations and innovations, and last but not least, incorporates complexity that gives the ecosystem resilience. The work demonstrates, through its focus on South Africa’s evidence ecosystem, that the global movement has much to learn from the South.
A human in vitro platform for the evaluation of pharmacology strategies in cardiac ischemia
Authors: Oleaga Carlota , Jalilvand Golareh , Legters Gregg , Martin Candace , Ekman Gail , McAleer Christopher W. , Long Christopher J. , Hickman James J.
Published: August 2019

Cardiac ischemic events increase the risk for arrhythmia, heart attack, heart failure, and death and are the leading mortality condition globally. Reperfusion therapy is the first line of treatment for this condition, and although it significantly reduces mortality, cardiac ischemia remains a significant threat. New therapeutic strategies are under investigation to improve the ischemia survival rate; however, the current preclinical models to validate these fail to predict the human outcome. We report the development of a functional human cardiac in vitro system for the study of conduction velocity under ischemic conditions. The system is a bioMEMs platform formed by human iPSC derived cardiomyocytes patterned on microelectrode arrays and maintained in serum-free conditions. Electrical activity changes of conduction velocity, beat frequency, and QT interval (the QT-interval measures the period from onset of depolarization to the completion of repolarization) or action potential length can be evaluated over time and under the stress of ischemia. The optimized protocol induces >80% reduction in conduction velocity, after a 4 h depletion period, and a partial recovery after 72 h of oxygen and nutrient reintroduction. The sensitivity of the platform for pharmacological interventions was challenged with a gap junction modulator (ZP1609), known to prevent or delay the depression of conduction velocity induced by ischemic metabolic stress. ZP1609 significantly improved the drastic drop in conduction velocity and enabled a greater recovery. This model represents a new preclinical platform for studying cardiac ischemia with human cells, which does not rely on biomarker analysis and has the potential for screening novel cardioprotective drugs with readouts that are closer to the measured clinical parameters.
Powering the 21st century by wind energy—Options, facts, figures
Authors: Rohrig K. , Berkhout V. , Callies D. , Durstewitz M. , Faulstich S. , Hahn B. , Jung M. , Pauscher L. , Seibel A. , Shan M. , Siefert M. , Steffen J. , Collmann M. , Czichon S. , Dörenkämper M. , Gottschall J. , Lange B. , Ruhle A. , Sayer F. , Stoevesandt B. , Wenske J.
Published: August 2019

This review article aims to provide an overview and insight into the most relevant aspects of wind energy development and current state-of-the-art. The industry is in a very mature stage, so it seems to be the right time to take stock of the relevant areas of wind energy use for power generation. For this review, the authors considered the essential aspects of the development of wind energy technology: research, modeling, and prediction of wind speed as an energy source, the technology development of the plants divided into the mechanical and electrical systems and the plant control, and finally the optimal plant operation including the maintenance strategies. The focus is on the development in Europe, with a partial focus on Germany. The authors are employees of the Fraunhofer Institutes, Institute for Energy Economics and Energy Systems Technology and Institute for Wind Energy Systems, who have contributed to the development of this technology for decades.
Detection of self-organized criticality behavior in an electronic circuit designed to solve a third order non-linear ODE (NL-ODE) for a damped KdV equation
Authors: Jha Amit Kumar , Banerjee Debasmita , Iyengar A. N. Sekar , Janaki M. S.
Published: August 2019

In this work, we present an electronic implementation of a damped Korteweg-de Vries equation modeled as a third order nonlinear autonomous ordinary differential equation (jerk equation). The circuit has been realized using operational amplifiers, multipliers, and passive electronic components which provides the time series solution of the equation in agreement with the numerical simulation results. Using nonlinear time series analysis on the acquired waveform data, we have obtained different types of phase space portraits and further analysis reflected long range correlation in the chaotic time series. Important findings include hysteresis induced bifurcation and self-organized criticality behavior in the system which is mentioned in this work.
Competitive networks using chaotic circuits with hierarchical structure
Authors: Uwate Y. , Nishio Y.
Published: August 2019

Coupled oscillatory systems are good models that are able to describe a variety of higher dimensional nonlinear phenomena. Coupled chaotic circuits produce many kinds of interesting synchronization phenomena. In recent years, research studies on complex networks related to the synchronization of coupled oscillators have attracted much attention. In the real world, there are a variety of different network structures. We focus on the competitive interaction network that includes conflict between two networks. Here, we propose a new paradigm for this competitive interaction network using coupled chaotic circuits.
V-ONSET (Vertical Octagonal Noncorrosive Stirred Energetic Turbulence): A vertical water tunnel with a large energy dissipation rate to study bubble/droplet deformation and breakup in strong turbulence
Authors: Masuk Ashik Ullah Mohammad , Salibindla Ashwanth , Tan Shiyong , Ni Rui
Published: August 2019

A vertical water tunnel facility has been constructed to study the dynamics of turbulent multiphase flow. The new system features several unique designs that allow us to study bubble deformation and breakup in strong turbulence: (i) The mean flow can be adjusted to balance the rising velocity of buoyant bubbles/droplets so that they can stay in the view area for an extended period of time. (ii) Turbulence is generated and controlled using a 3D-printed jet array that can fire 88 random high-speed momentum jets with the individual jet velocity of up to 12 m/s. This component allows us to attain turbulence with a high energy dissipation rate (≥0.1 m2/s3), which is orders-of-magnitude higher than most of the existing turbulent multiphase flow facilities. (iii) Turbulence generated in the test section is nearly homogeneous and isotropic, and the turbulent fluctuations are also decoupled from the mean flow. The resulting turbulence intensity can be varied between 20% and 80% with the speed of the mean flow at around 0.2 m/s. (iv) This system has an octagonal test section that allows six cameras to image and reconstruct the 3D shape of deforming bubbles/droplets in turbulence. The same set of cameras was also used for tracking tracers in the surrounding turbulent flow. Both the reconstruction and particle tracking were completed using our in-house codes that were parallelized to run on high-performance computing clusters efficiently.
Local mechanical and electrical behavior in CdTe thin film solar cells revealed by scanning probe microscopy
Authors: Mathews Melissa , Guo Liping , Han Xiao , Saurav Swapnil , Xing Guozhong , Li Lin , Yan Feng
Published: August 2019

The nanoscale electrical and mechanical properties in the CdTe thin films solar cells were investigated using the scanning probe microscopy. The comparative localized electrical and mechanical properties between as-grown and CdCl2 treated CdTe thin films for the grain and grain boundaries were studied using the conductive atomic force microscopy (cAFM) and force modulation microscopy (FMM). An increased electrical behavior and decreased elastic stiffness in the CdCl2 treated thin films were recorded to elucidate the impact from the grain growth of CdTe grains. On applying a simulated working electrical bias into the CdTe thin-film solar cells, the electric field across the CdTe film can increase the softness of CdTe thin film. The results imply the presence of a potential mechanical failure site in the CdTe grain boundary, which may lead to device degradation.
The ejecting lamella of impacting compound droplets
Authors: Liu Dongdong , Tran Tuan
Published: August 2019

Impacting dynamics of compound droplets consisting of oil and water–glycerol mixture transitions from spreading to splashing with an increasing volumetric oil-mixture ratio. The transition to splashing is directly related to the dynamics of the ejecting lamella upon impact. Here, we present a detailed study of the ejecting lamella at the early stage of the impact. We experimentally characterize the ejection velocity and time of the ejecting lamella for a wide range of impacting velocities, volumetric oil ratios, and viscosities of the mixture. We show that ejecting dynamics depends significantly on the volumetric oil-mixture ratio, while it is slightly affected by the viscosity of the mixture. We also propose and verify experimentally a predictive model for the ejection velocity and time of the lamella.
A simplified account of the correlation effects to bond breaking processes: The Brillouin-Wigner perturbation theory using a multireference formulation
Authors: Manna Shovan , Ray Suvonil Sinha , Chattopadhyay Sudip , Chaudhuri Rajat K.
Published: August 2019

Adaptation of improved virtual orbital complete active space configuration interaction functions in state-specific multireference perturbation theory motivated by the Brillouin-Wigner perturbation scheme using Møller-Plesset multipartitioning is examined. The method, denoted as IVO-BWMRPT, focuses on only the root of principal interest at a time using single-root parameterization of Jeziorski-Monkhorst ansatz within the frame of an effective Hamiltonian. This approach yields size-extensive energy and avoids intruder-state problems in a natural manner. It allows relaxation of the reference space wave function in the presence of the perturbation which produces an important differential effect on the energy and cannot be neglected for quasidegenerate electronic states. The method has been tested against nontrivial situations such as the Be + H2 insertion profile along with the energy surfaces of FH and X2 (X = F, Cl, and Br), in which conventional single-reference methods generally fail, exhibiting very encouraging findings. We also consider the energy surfaces of ethylene (by breaking the π bond as well as the CC bond) and for the twisting of tetramethyleneethane. IVO-BWMRPT represents a rather balanced protocol for the description of molecules at a wide range of geometries, including stretched or dissociating bonds. Close agreement of our estimates with the reference values provides a useful measure for the success of the IVO-BWMRPT method to treat strongly correlated systems. Our results for TME show that the singlet state always lies below the triplet state for different conformations. The IVO-BWMRPT furnishes a compact and correct representation of the MR-wave function, and hence, a large variety of quasidegenerate situations can be accommodated within the method.
On-off intermittency and hard turbulence in the flow of fluid in the magnetic field
Authors: Belyaev I. A. , Biryukov D. A. , Gerasimov D. N. , Yurin E. I.
Published: August 2019

This work provides an analysis of experiments in which various modes of mercury flow in a constant external magnetic field were observed; we examined the temperature oscillations in the mercury flow in a heated pipe at various Reynolds and Hartmann numbers. In some modes, the temperature oscillations have specific forms of strong aperiodic “bursts” over the weak irregular background, which are specific to the developed turbulent flow. To determine the nature of these temperature oscillations and the characteristics of the fluid flow, we examined them through the apparatus of nonlinear dynamics. The totality of all the results (autocorrelation function, correlation integral, maximum Lyapunov exponents, and Fourier transform) provide evidence of the chaotic nature of the observed flow modes despite the relative weakness of high-frequency harmonics in comparison to low-frequency ones. In the case of separate bursts of turbulence, the duration of the laminar phase τ follows the known distribution ∼τ–3/2, derived from the theory of on-off intermittency.
Tailoring low energy electron absorption via surface nano-engineering of cesiated chromium films
Authors: Fernandes Cauduro Andre L. , Hess Lucas H. , Ogletree D. Frank , Schwede Jared W. , Schmid Andreas K.
Published: August 2019

In this letter, we demonstrate that improved low energy electron absorption is achieved by suppressing the crystallinity of chromium thin-films grown on W[110], which points to a promising route for achieving highly efficient thermionic energy converters. Using low energy electron microscopy (LEEM) and in situ film growth, we show that substrate temperature control permits well-controlled fabrication of either epitaxial Cr[110] films or nanocrystalline Cr layers. We show that the work function of cesium saturated nanocrystalline Cr thin-films is ∼0.20 eV lower than that of epitaxial Cr[110] films. Our LEEM measurements of absorbed and reflected currents as a function of electron energy demonstrate that nanocrystallinity of cesiated chromium films results in 96% electron absorption in the range up to 1 eV above the work function, compared to just 79% absorption in cesiated crystalline Cr[110] films. These results point to metal films with suppressed crystallinity as an economical and scalable means to synthesize nanoengineered surfaces with optimized properties for next generation anode materials in high performance thermionic energy converters.
A multiscale procedure based on the stochastic kinetic mean field and the phase-field models for coarsening
Authors: Gajdics Bence , Tomán János J. , Zapolsky Helena , Erdélyi Zoltán , Demange Gilles
Published: August 2019

We report a quantitative multiscale (MS) procedure based on the recently developed Stochastic Kinetic Mean Field approach (SKMF) [Erdélyi, M. Pasichnyy, V. Bezpalchuk, J. J. Tomán, B. Gajdics, and A. M. Gusak, Comput. Phys. Commun. 204, 31–37 (2016)], combined with the Phase Field model (PFM) and CALPHAD database, to study the nucleation-growth-coarsening process in alloys. The SKMF approach reproduces the nucleation and early growth of precipitates in the matrix, and the PFM then simulates the coarsening of the microstructure. To ensure the consistency of the procedure, the length and time scales of SKMF and PFM are explicitly connected. Moreover, both the effective interaction energies used in the SKMF and the free energy used in the PFM are taken from CALPHAD database. Two different implementations of the procedure are proposed. First, the postnucleation microstructure as provided by SKMF is used as the initial condition for subsequent PFM simulations. Second, only the particle size distribution and particle density are transferred to PFM, thereby giving access to bigger systems. The proposed procedure is tested in the specific case of the Ag-Cu model alloy.
The third law of thermodynamics in open quantum systems
Authors: Shastry Abhay , Xu Yiheng , Stafford Charles A.
Published: August 2019

We consider open quantum systems consisting of a finite system of independent fermions with arbitrary Hamiltonian coupled to one or more equilibrium fermion reservoirs (which need not be in equilibrium with each other). A strong form of the third law of thermodynamics, S(T) → 0 as T → 0, is proven for fully open quantum systems in thermal equilibrium with their environment, defined as systems where all states are broadened due to environmental coupling. For generic open quantum systems, it is shown that S(T) → g ln 2 as T → 0, where g is the number of localized states lying exactly at the chemical potential of the reservoir. For driven open quantum systems in a nonequilibrium steady state, it is shown that the local entropy Sx;T→0 as T(x) → 0, except for cases of measure zero arising due to localized states, where T(x) is the temperature measured by a local thermometer.
The effect of external temperature gradients on thermal conductivity in non-equilibrium molecular dynamics simulations: From nanowires to bulk Si
Authors: Zhang Enrui , Yao Yunpeng , Gao Tianyu , Kang Dongdong , Wu Jianhua , Dai Jiayu
Published: August 2019

Nonequilibrium molecular dynamics is widely used to calculate the thermal conductivity of various materials, but the influence of temperature gradient to thermal conductivity has received limited attention within current research studies. The purpose of this article is to explore the discrepancy between intrinsic and extrinsic thermal conductivities under different temperature gradients, which can be considered as external fields. The analyses of phonon density of states have shown that the temperature gradient plays a role in the external field, and a larger temperature gradient activates more low-frequency vibrational modes, which leads to larger thermal conductivities. Specially, the thermal conductivity increases linearly with the temperature gradient when using Stillinger-Weber (SW) potential. Moreover, a new formula was derived to satisfactorily fit the thermal conductivities of bulk Si and silicon nanowires (SiNWs) for various cell sizes, and the physical meaning of the formula was explained. It is shown that the SW potential and Tersoff potential of Si produce different thermal conductivities. By comparing the results of first principles simulations, the Tersoff potential gives rise to better description of vibrational modes.
Compatibility of advanced water models with a united atom model of lipid in lipid bilayer simulation
Authors: Erimban Shakkira , Daschakraborty Snehasis
Published: August 2019

Molecular dynamics simulation of lipid bilayers generally uses all-atom, united-atom, and coarse-grained models of lipid molecules. The GROMOS united-atom model of lipid constructs a balance between accuracy and computational cost. The above-mentioned model satisfactorily reproduces many of the structural and dynamical properties of different lipid bilayers. However, the GROMOS force field is parameterized only with the SPC model of water. Unfortunately, SPC is not an excellent model of water for predicting the structure and dynamics of the interfacial water near the lipid bilayer. More advanced water models, such as TIP3P-FB and TIP4P-FB, outperform the SPC model in predicting different thermodynamic and microscopic properties of bulk water. This motivates us to check the compatibility of five different water models, including SPC, with the GROMOS96 53A6L united atom model of two different lipid bilayers, DPPC and POPC. A systematic comparison of the bilayer structure and dynamics, resulting from the simulations with different water models, is done. We find general agreement of the results for different water models with the experiment. In fact, the more advanced water models provide better agreement with the experiment. This study, therefore, helps in widening the range of choice of water models in simulating the lipid bilayer using the GROMOS united-atom model of the lipid molecules.
Langmuir probe electronics upgrade on the tokamak à configuration variable
Authors: De Oliveira H. , Marmillod P. , Theiler C. , Chavan R. , Février O. , Labit B. , Lavanchy P. , Marlétaz B. , Pitts R. A. ,   TCV team
Published: August 2019

A detailed description of the Langmuir probe electronics upgrade for TCV (Tokamak à Configuration Variable) is presented. The number of amplifiers and corresponding electronics has been increased from 48 to 120 in order to simultaneously connect all of the 114 Langmuir probes currently mounted in the TCV divertor and main-wall tiles. Another set of 108 amplifiers is ready to be installed in order to connect 80 new probes, built in the frame of the TCV divertor upgrade. Technical details of the amplifier circuitry are discussed as well as improvements over the first generation of amplifiers developed at SPC (formerly CRPP) in 1993/1994 and over the second generation developed in 2012/2013. While the new amplifiers have been operated successfully for over a year, it was found that their silicon power transistors can be damaged during some off-normal plasma events. Possible solutions are discussed.
Generation of a microwave beam with both orbital and spin angular momenta using a transparent metasurface
Authors: Shi Hongyu , Wang Luyi , Chen Xiaoming , Zhang Anxue , Xu Zhuo
Published: August 2019

In this paper, transparent metasurfaces generating microwave beams with both orbital angular momentum (OAM) and spin angular momentum (SAM) are proposed. A multilayered metasurface unit cell was designed for simultaneously manipulating the transmission phase and polarization state of a linearly polarized incident wave around 4.6 GHz. Using such unit cell design, the proposed metasurfaces can introduce additional SAM and OAM to the transmitted wave by linear-to-circular polarization conversion and vortex transmission phase distributions. The simulation and measurement results are in good agreement with each other and demonstrate the generation of microwave beams with both OAM and SAM.
Plasticity facilitates pattern selection of networks of chemical oscillations
Authors: Sebek Michael , Kiss István Z.
Published: August 2019

Rotating wave synchronization patterns are explored with a ring of 20 electrochemical oscillators during nickel electrodissolution in sulfuric acid. With desynchronized initial states, coupling alone yields predominance of nonrotating solutions, i.e., in-phase synchronization. An experimental technique is presented in which, through a combination of temporary alterations in topology, the application of global feedback provides rotational solutions. With phase repulsive global feedback, the in-phase synchronization is destabilized and a rotating wave is obtained. This feedback induced rotating wave can be employed to establish an initial condition for the rotating wave with coupling only. Higher order rotating solutions with 2, 3, and 4 waves corotating around the ring are observed, where the initial conditions are generated by temporary network rewiring to a structure with 2, 3, and 4 loops, respectively, and by global feedback. The experimental observations are supported by numerical simulations with a phase model. The results indicate that while network plasticity is thought to be significant in the operation of neural systems, it can also play a role in pattern selection of chemical systems.
The effect of various tax and redistribution models on the Gini coefficient of simple exchange games
Authors: Kulp Christopher W. , Kurtz Michael , Wilston Nathaniel , Quigley Luke
Published: August 2019

The Bennati-Drăgulescu-Yakovenko (BDY) game is an agent-based simple exchange game that models a basic economic system. The BDY game results in the agents’ wealth following a Boltzmann-Gibbs distribution. In other words, the result of the game is many “poor” agents and few “wealthy” agents. In this paper, we apply several tax and redistribution models to study their effect on the population’s wealth distribution by computing the resulting Gini coefficient of the system. We find that income taxes, both flat and progressive, that evenly redistributed taxed monies do little to change the Gini coefficient from the Boltzmann-Gibbs distribution. However, income taxes that are redistributed to the poorest agents can significantly lower the Gini coefficient, resulting in a more evenly distributed wealth distribution. Furthermore, we find that a very small wealth tax can lead to significant decreases in the Gini coefficient.
Stability of hydrogen atom in non-ideal classical plasmas
Authors: Das Biswajit , Karmakar Akashdip , Ghoshal Arijit
Published: August 2019

The stability of a hydrogen atom embedded in classical nonideal plasma has been investigated. The interaction potential between the proton and the electron has been modeled by a pseudopotential, which is obtained from a sequential solution of Bogolyubov chain equations. The critical values of the plasma screening parameters have been determined quite accurately within the framework of the Rayleigh-Ritz variational method by employing an extensive wave function following a definitive prescription. Convergence of the results has been corroborated by increasing the number of terms in the wave function. A detailed study has been carried out on the effects of nonideality of plasma on the bound states for the density and temperature lying in the ranges of 2.7 × [1023–1026] m−3 and [104–105] K, respectively. It is found that the atom remains bound in the aforementioned density and temperature ranges.
Fabrication of superhydrophilic surface on metallic nickel by sub-nanosecond laser-induced ablation
Authors: Zhu HuaZhong , Zhang HongChao , Ni XiaoWu , Shen ZhongHua , Lu Jian
Published: August 2019

The alterations of wettability on metallic nickel surface by sub-nanosecond laser (1 ns, 1064 nm) induced surface modification was investigated. An approximate linear relation between surface contact angles (CAs) and accumulated fluence was established, which shows that with proper combinations of laser parameters, CA would reduce significantly from its initial value (∼96°) to approximately 3.1°. The microscopic inspection and roughness test reveal that the surface roughness on irradiated areas would increase remarkably due to the distribution of micro/nanoparticels and cracks that induced by laser ablation, which consequently improve the hydrophilic performance effectively. On the other hand, elemental analyses by use of XPS demonstrate that the nickel dioxides and nickel hydroxides were generated as the main components covering the self-organized structures. Such increasement in oxygen content, especially the growth of NiO and hydroxyl group provides a prerequisite in the transformation of nickel from initial hydrophobicity to hydrophilicity. And the integrated effects of surface morphology, roughness and chemistry ultimately led to the formation of super-wettability. The investigation indicates that, the sub-nanosecond laser is an effective tool to transform the metallic nickel into functional material with a highly hydrophilic surface by creating controllable topographical features and chemical properties on its surface.
Realistic model of charge mobility in π-conjugated polymer systems
Authors: Berencei Laszlo , Grout-Smith Alice , Poole Jessica Ellen , Barford William
Published: August 2019

Charge transfer processes and charge mobility are investigated in the poly(p-phenylenevinylene) model system. Realistic disordered polymer conformations are created and used in a coarse-grained model. Localized and quasiextended states are obtained using the Holstein Hamiltonian. Charge transport is modeled as an incoherent hopping mechanism in the framework of unimolecular and bimolecular Marcus theory for intramolecular and intermolecular processes, respectively, to account for the electron-phonon coupling present in π-conjugated polymer systems. Static and quasidynamic disorder effects are both considered using the “fluctuating bridges” approach. Charge mobility is calculated using kinetic Monte Carlo simulations for a range of physically relevant parameters. We examine the relative importance of intramolecular and intermolecular mechanisms and the role of localized and extended states in the transport process. We discuss the role of disorder and temperature and show that a log μ∝−F electric field dependence in the high field regime naturally emerges from our model. We show that disorder significantly reduces the mobility at low fields but slightly increases it at high fields. We also show that the mobility is dominated by interchain charge transfer between low energy localized states at low fields, but at higher fields, intrachain transfer to more delocalized higher energy states becomes equally important. This crossover is the cause of anisotropic charge mobility at intermediate field strengths.
Equation of state and force fields for Feynman–Hibbs-corrected Mie fluids. I. Application to pure helium, neon, hydrogen, and deuterium
Authors: Aasen Ailo , Hammer Morten , Ervik Åsmund , Müller Erich A. , Wilhelmsen Øivind
Published: August 2019

We present a perturbation theory that combines the use of a third-order Barker–Henderson expansion of the Helmholtz energy with Mie-potentials that include first- (Mie-FH1) and second-order (Mie-FH2) Feynman–Hibbs quantum corrections. The resulting equation of state, the statistical associating fluid theory for Mie potentials of variable range corrected for quantum effects (SAFT-VRQ-Mie), is compared to molecular simulations and is seen to reproduce the thermodynamic properties of generic Mie-FH1 and Mie-FH2 fluids accurately. SAFT-VRQ Mie is exploited to obtain optimal parameters for the intermolecular potentials of neon, helium, deuterium, ortho-, para-, and normal-hydrogen for the Mie-FH1 and Mie-FH2 formulations. For helium, hydrogen, and deuterium, the use of either the first- or second-order corrections yields significantly higher accuracy in the representation of supercritical densities, heat capacities, and speed of sounds when compared to classical Mie fluids, although the Mie-FH2 is slightly more accurate than Mie-FH1 for supercritical properties. The Mie-FH1 potential is recommended for most of the fluids since it yields a more accurate representation of the pure-component phase equilibria and extrapolates better to low temperatures. Notwithstanding, for helium, where the quantum effects are largest, we find that none of the potentials give an accurate representation of the entire phase envelope, and its thermodynamic properties are represented accurately only at temperatures above 20 K. Overall, supercritical heat capacities are well represented, with some deviations from experiments seen in the liquid phase region for helium and hydrogen.
Flow and heat transfer characteristics of a nanofluid between a square enclosure and a wavy wall obstacle
Authors: Chandra Roy Nepal
Published: August 2019

A mathematical model for the natural convection flow and heat transfer of a nanofluid in an annulus enclosed by a square cylinder and a wavy wall cylinder is developed. Using vorticity-stream function formulation, we first derive governing equations in the Cartesian coordinates. Then, these equations are transformed utilizing coordinate transformations into a system of equations valid for the present physical domain. The problem is solved using the finite difference method. It is found that for higher values of the volume fraction of nanoparticles, the number of undulations of the wavy wall of the inner cylinder and Rayleigh number, the strength of streamlines significantly increases. However, the amplitude of undulations diminishes the intensity of streamlines. The isotherms are also strongly influenced by these parameters. Contrary to this, the Nusselt number at the inner and outer cylinders is remarkably increased due to the increase of the volume fraction of nanoparticles, amplitude of undulations, and Rayleigh number. For the higher volume fraction of nanoparticles and Rayleigh number, the average Nusselt number at the inner and outer cylinders is higher. The maximum and minimum values of the velocity profile increase with the higher Rayleigh number. Nevertheless, the converse scenario is observed for the larger amplitude of undulation and volume fraction of nanoparticles. The temperature near the inner cylinder noticeably decreases with the increase of the Rayleigh number, whereas it slowly reduces for higher amplitude of undulations. Above all, this investigation might be helpful for the researchers in regard to the approach of making a more complex geometry by using coordinate transformations. Furthermore, the results could provide vital information about the problems in current technological applications.
Reynolds number effect on drag control via spanwise wall oscillation in turbulent channel flows
Authors: Yao Jie , Chen Xi , Hussain Fazle
Published: August 2019

The effect of Reynolds number (Reτ) on drag reduction using spanwise wall oscillation is studied through direct numerical simulation of incompressible turbulent channel flows with Reτ ranging from 200 to 2000. For the nondimensional oscillation period T+ = 100 with maximum velocity amplitude A+ = 12, the drag reduction (DR) decreases from 35.3% ± 0.5% at Reτ = 200 to 22.3% ± 0.7% at Reτ = 2000. The oscillation frequency ω+ for maximum DR slightly increases with Reτ, i.e., from ω+ ≈ 0.06 at Reτ = 200 to 0.08 at Reτ = 2000, with DRmax=23.2%±0.6%. These results show that DR progressively decreases with increasing Reτ. Turbulent statistics and coherent structures are examined to explain the degradation of drag control effectiveness at high Reτ. Fukagata, Iwamoto, and Kasagi analysis in combination with the spanwise wavenumber spectrum of Reynolds stresses reveals that the decreased drag reduction at higher Reτ is due to the weakened effectiveness in suppressing the near-wall large-scale turbulence, whose contribution continuously increases due to the enhanced modulation and penetration effect of the large-scale and very large-scale motions in the log and outer regions. Both the power-law model (DR∝Reτ−γ) and the log-law model [DR = f(Reτ, ΔB), where ΔB is the vertical shift of the log-law intercept under control] are examined here by comparing them with our simulation data, from these two models we predict more than 10% drag reduction at very high Reynolds numbers, say, Reτ = 105.
Defect-rich single-layer MoS2 nanosheets with high dielectric-loss for contrast-enhanced thermoacoustic imaging of breast tumor
Authors: Li Yaping , Tan Qihao , Qin Huan , Xing Da
Published: August 2019

Microwave induced thermoacoustic imaging (MTAI), combining high contrast of tissue dielectric absorption and high resolution of ultrasonography, is a potential nonionizing candidate for breast tumor detection. In this work, defect-rich single-layer molybdenum disulfide (S-MoS2) nanosheets with high dielectric-loss were developed for enhancement of thermoacoustic (TA) contrast. The underlying mechanism involves a large number of Mo and S atom vacancies on the prepared S-MoS2 nanosheets. The distribution of electron clouds around the vacancies is uneven, thus creating a defect electric dipole. With pulsed microwaves, the defect electric dipoles were repeatedly polarized at gigahertz. This results in a transient heating and thermoelastic expansion yielding a TA wave. The results confirm that the defect-rich S-MoS2 nanosheets can produce a stronger TA signal with significantly enhanced contrast than the commonly used TA probes on a per mass basis. The feasibility of the MoS2 nanosheets was evaluated with a model of breast tumor. The results demonstrate that defect-rich S-MoS2 nanosheets are promising candidates for breast tumor imaging.
Tunable acoustic valley edge states in a flow-free resonator system
Authors: Liu Xingxing , Guo Qiuquan , Yang Jun
Published: August 2019

Recent developments in valleytronic materials have inspired developing various analogs of acoustic crystal systems for manipulating airborne acoustic transmissions. Earlier designs of acoustic topological insulators were normally characterized by untunable bulky geometries and a narrow effective frequency response, which limited the design and development of practical acoustic devices. Here, we design a gapless topologically protected acoustic resonator system based on valley edge states in reconfigurable phononic crystals. By simply rotating the modified spiral springs to adjust the inner radius without altering the lattice structure, this method can be utilized to realize backscattering immune, tunable, broadband, and miniaturized functional acoustic applications. This study offers a design route in valley phenomena for acoustic topological flow-free resonator systems.
Room temperature ferrimagnetism in Yb-doped relaxor ferroelectric PbFe2/3W1/3O3
Authors: Joshi D. C. , Ivanov S. A. , Bush A. A. , Sarkar T. , Ye Z.-G. , Nordblad P. , Mathieu R.
Published: August 2019

We report ferrimagnetism and reentrant relaxor ferroelectricity near room temperature in a Yb-doped PbFe2/3W1/3O3 cubic perovskite. Structural analysis reveals the presence of a single cubic perovskite phase, with the Fm3¯m space group [lattice parameter: a = 8.0112(3) Å], and partial B-site ordering. The B-site ordering yields uncompensated magnetic moments in the antiferromagnetic structure of PbFe2/3W1/3O3 and ferrimagnetism near room temperature. An excess moment of ∼0.6 μB/B-site may be estimated from magnetic hysteresis curves recorded up to 50 kOe at 5 K. The temperature dependent magnetodielectric study reveals a sequential phase transition from a long-range ferroelectric state (across 280 K) to a short-range relaxor ferroelectric state (across 190 K). The long-range ferroelectric ordering is found to be more affected by the application of external magnetic fields than the relaxor phase.
Two-layer Gaussian-based MCTDH study of the S1 ← S vibronic absorption spectrum of formaldehyde using multiplicative neural network potentials
Authors: Koch Werner , Bonfanti Matteo , Eisenbrandt Pierre , Nandi Apurba , Fu Bina , Bowman Joel , Tannor David , Burghardt Irene
Published: August 2019

The absorption spectrum of the vibronically allowed S1(1A2) ← S0(1A1) transition of formaldehyde is computed by combining multiplicative neural network (NN) potential surface fits, based on multireference electronic structure data, with the two-layer Gaussian-based multiconfiguration time-dependent Hartree (2L-GMCTDH) method. The NN potential surface fit avoids the local harmonic approximation for the evaluation of the potential energy matrix elements. Importantly, the NN surface can be constructed so as to be physically well-behaved outside the domain spanned by the ab initio data points. A comparison with experimental results shows spectroscopic accuracy of the converged surface and 2L-GMCTDH quantum dynamics.
Manifestation of the electromagnetic proximity effect in superconductor-ferromagnet thin film structures
Authors: Flokstra M. G. , Stewart R. , Satchell N. , Burnell G. , Luetkens H. , Prokscha T. , Suter A. , Morenzoni E. , Langridge S. , Lee S. L.
Published: August 2019

Using the newly emerged theory model of an electromagnetic proximity effect, we demonstrate that it provides a good description of our previously reported anomalous Meissner screening observed in thin film superconductor-ferromagnet proximity structures. Using the low energy muon spin rotation measurement technique, we further investigate this new theory by probing directly the flux screening in various superconductor-ferromagnet proximity structures. We examine its main characteristics and find in general good agreement between theory and experiment. Understanding and control of this new proximity effect is an important step forward toward a new generation of superconducting spintronic devices.
Observation of the onset of torsion-induced, mode-specific dissipative intramolecular vibrational redistribution (IVR)
Authors: Kemp David J. , Tuttle William D. , Gardner Adrian M. , Whalley Laura E. , Wright Timothy G.
Published: August 2019

Evidence is found showing that coupling with vibration-torsion (“vibtor”) levels of both in-plane and out-of-plane vibrations is instrumental in causing dissipative intramolecular vibrational redistribution (IVR). Both zero-electron-kinetic-energy (ZEKE) spectroscopy and two-dimensional laser-induced fluorescence (2D-LIF) spectroscopy are employed to investigate a series of bands located ∼1200 cm−1 above the S1 ← S0 origin in p-fluorotoluene. Transitions in this wavenumber region have been the focus of a number of studies probing IVR. By recording both ZEKE and 2D-LIF spectra, a prepared S1 population is projected onto both the ground state cation and ground state neutral energy states, respectively, giving added confidence to the assignments. The spectral region under discussion is dominated by a pair of fundamental bands, but for the first time, we present explicit evidence that this is complicated by contributions from a number of overtones and combinations, including vibtor levels. We deduce that very different extents of coupling are present across a 60 cm−1 window of the spectrum, even though the density of states is similar; in particular, one of the fundamentals couples efficiently to the increasing bath of levels, while one does not. We explain this by the influence of serendipitous near-coincidences of same-symmetry levels.
Asymmetric bipolar switch device for electrochemical processes
Authors: Gonzalez-Vogel Alvaro , Rojas Orlando J.
Published: August 2019

New strategies for the intensification of industrial electromembrane processes are needed, especially to reduce equipment size and operational costs. To intensify those processes and to decrease fouling and scale occurrence in such systems, we propose operation with very short asymmetric pulses (order of microseconds) of alternating polarity. Hence, a custom made Asymmetric Bipolar Switch was designed and built, operating with pulse widths in the 10-5-10-2 s range. Compared to traditional systems, we demonstrate the possibility of applying pulses with high intensities, up to three times higher than normal operation, using a frequency range between 0 (continuous operation) and 102 Hz. The proposed device was coupled to an electrodialysis cell for desalting a brine solution. When switching in desalination, a Back Electrochemical Force was identified, which could affect the integrity of the electronic systems due to spikes of reverse voltage. Hence, mitigation strategies were applied by changing the switching logic and incorporating new elements in the circuitry, similar to those in breaking methods in electrical motors. While desalting in electrodialysis, the experiments showed a limited power loss, up to 0.6% of the total power applied, attributed mainly to electrical disturbance (conduction and switching losses in the electronic components were minor at this scale). No significant variation in the desalination performance was observed at low current densities. The designed Asymmetric Bipolar Switch opens new possibilities for the operation with electromembranes and other electrochemical processes.
Nano-indentation and avalanches in compressed porous SiO2
Authors: Beirau Tobias , Salje Ekhard K. H.
Published: August 2019

The “nano-indentation continuous stiffness measurement technique” has been employed to analyze the failure dynamics of mesoporous SiO2 based material (Vycor). The depth dependence of the indentation hardness (H), elastic modulus (E), and elastoplastic parameter (S2/P) shows crackling noise, which has been analyzed to monitor the jerky strain release. The noise is power law distributed with exponents near ∼1.5 over several decades, confirming avalanche criticality. This value is in good agreement with literature results obtained by other techniques and with earthquake statistics.
Efficient heating of single-molecule junctions for thermoelectric studies at cryogenic temperatures
Authors: Gehring Pascal , van der Star Martijn , Evangeli Charalambos , Le Roy Jennifer J. , Bogani Lapo , Kolosov Oleg V. , van der Zant Herre S. J.
Published: August 2019

The energy dependent thermoelectric response of a single molecule contains valuable information about its transmission function and its excited states. However, measuring it requires devices that can efficiently heat up one side of the molecule while being able to tune its electrochemical potential over a wide energy range. Furthermore, to increase junction stability, devices need to operate at cryogenic temperatures. In this work, we report on a device architecture to study the thermoelectric properties and the conductance of single molecules simultaneously over a wide energy range. We employ a sample heater in direct contact with the metallic electrodes contacting the single molecule which allows us to apply temperature biases up to ΔT = 60 K with minimal heating of the molecular junction. This makes these devices compatible with base temperatures Tbath < 2 K and enables studies in the linear (ΔT≪Tmolecule) and nonlinear (ΔT≫Tmolecule) thermoelectric transport regimes.
Realistic atomic structure of fly ash-based geopolymer gels: Insights from molecular dynamics simulations
Authors: Lyngdoh Gideon A. , Kumar Rajesh , Krishnan N. M. Anoop , Das Sumanta
Published: August 2019

Geopolymers, synthesized through alkaline activation of aluminosilicates, have emerged as a sustainable alternative for traditional ordinary Portland cement. In spite of the satisfactory mechanical performance and sustainability-related benefits, the large scale acceptance of geopolymers in the construction industry is still limited due to poor understanding of the composition-property relationships. Molecular simulation is a powerful tool to develop such relationships, provided that the adopted molecular structure represents the experimental data effectively. Toward this end, this paper presents a new molecular structure of sodium aluminosilicate hydrate geopolymer gels, inspired from the traditional calcium silicate hydrates gel. In contrast to the existing model—where water is uniformly distributed in the structure—we present a layered-but-disordered structure. This new structure incorporates water in the interlayer space of the aluminosilicate network. The structural features of the new proposed molecular structure are evaluated in terms of both short- and medium-range order features such as pair distribution functions, bond angle distributions, and structure factor. The structural features of the newly proposed molecular structure with interlayer water show better correlation with the experimental observations as compared to the existing traditional structure signifying an increased plausibility of the proposed structure. The proposed structure can be adopted as a starting point toward the realistic multiscale simulation-based design and development of geopolymers.