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We present a design for an atomic oven suitable for loading ion traps, which is operated via optical heating with a continuous-wave multimode diode laser. The absence of the low-resistance electrical connections necessary for Joule heating allows the oven to be extremely well thermally isolated from the rest of the vacuum system, and for an oven filled with calcium we achieve a number density suitable for rapid ion loading in the target region with ~200 mW of laser power, limited by radiative losses. With simple feedforward to the laser power, the turn-on time for the oven is less than 20 s, while the oven contains enough calcium to operate continuously for many thousands of years without replenishment., 7 pages, 5 figures

This work evaluates the applicability of super-resolution generative adversarial networks (SRGANs) as a methodology for the reconstruction of turbulent-flow quantities from coarse wall measurements. The method is applied both for the resolution enhancement of wall fields and the estimation of wall-parallel velocity fields from coarse wall measurements of shear stress and pressure. The analysis has been carried out with a database of a turbulent open-channel flow with a friction Reynolds number. We first show that SRGAN can be used to enhance the resolution of coarse wall measurements. If compared with the direct reconstruction from the sole coarse wall measurements, SRGAN provides better instantaneous reconstructions, in terms of both mean-squared error and spectral-fractional error. Even though lower resolutions in the input wall data make it more challenging to achieve highly accurate predictions, the proposed SRGAN-based network yields very good reconstruction results. Furthermore, it is shown that even for the most challenging cases, the SRGAN is capable of capturing the large-scale structures that populate the flow. The proposed novel methodology has a great potential for closed-loop control applications relying on non-intrusive sensing. R.V. acknowledges the support by the Göran Gustafsson Foundation. S.D. and A.I. acknowledge the support by the European Research Council, under the COTURB Grant No. ERC-2014.AdG-669505. H.A. acknowledges the support by Wallenberg AI, Autonomous Systems, and Software Program (WASP-AI). We would also like to acknowledge Hampus Tober for useful discussions throughout the present study.

This work has been partially funded by the Spanish Ministerio de Ciencia, Innovaci on y Universidades and the Agencia Estatal de Investigaci on through Grant Nos. MTM2017-84446-C2–2-R (A.L., E.M., and A.T.), FIS2017-84440-C2–2-P (A.T.), and FIS2016- 76359-P. (F.V.R.). M.A.L.C. and F.V.R. also acknowledge support from the regional Extremadura Government through Project Nos. GR18079 and IB16087. Computing facilities from the Extremadura Research Centre for Advanced Technologies (CETA-CIEMAT) are also acknowledged. All grants and facilities were provided with partial support from the ERDF., The data that support the findings of this study are available from the corresponding author upon reasonable request., We study a granular gas of viscoelastic particles (kinetic energy loss upon collision is a function of the particles’ relative velocities at impact) subject to a stochastic thermostat. We show that the system displays anomalous cooling and heating rates during thermal relaxation processes, this causing the emergence of thermal memory. In particular, a significant Mpemba effect is present, i.e., an initially hotter/cooler granular gas can cool down/heat up faster than an in comparison cooler/hotter granular gas. Moreover, a Kovacs effect is also observed, i.e., a nonmonotonic relaxation of the granular temperature—if the gas undergoes certain sudden temperature changes before fixing its value. Our results show that both memory effects have distinct features, very different and eventually opposed to those reported in theory for granular fluids under simpler collisional models. We study our system via three independent methods: approximate solution of the kinetic equation time evolution and computer simulations (both molecular dynamics simulations and direct simulation Monte Carlo method), finding good agreement between them., Extremadura Government GR18079,IB16087, Ministerio de Ciencia, Innovación y Universidades MCIU, European Regional Development Fund ERDF, Agencia Estatal de Investigación FIS2016-76359-P,FIS2017-84440-C2–2-P,MTM2017-84446-C2–2-R AEI

Magnetic heating, namely, the use of heat released by magnetic nanoparticles (MNPs) excited with a high-frequency magnetic field, has so far been mainly used for biological applications. More recently, it has been shown that this heat can be used to catalyze chemical reactions, some of them occurring at temperatures up to 700 °C. The full exploitation of MNP heating properties requires the knowledge of the temperature dependence of their heating power up to high temperatures. Here, a setup to perform such measurements is described based on the use of a pyrometer for high-temperature measurements and on a protocol based on the acquisition of cooling curves, which allows us to take into account calorimeter losses. We demonstrate that the setup permits to perform measurements under a controlled atmosphere on solid state samples up to 550 °C. It should in principle be able to perform measurements up to 900 °C. The method, uncertainties, and possible artifacts are described and analyzed in detail. The influence on losses of putting under vacuum different parts of the calorimeter is measured. To illustrate the setup possibilities, the temperature dependence of heating power is measured on four samples displaying very different behaviors. Their heating power increases or decreases with temperature, displaying temperature sensibilities ranging from -2.5 to +4.4% K-1. This setup is useful to characterize the MNPs for magnetically heated catalysis applications and to produce data that will be used to test models permitting to predict the temperature dependence of MNP heating power., The authors acknowledge the ERC Advanced Grant (No. MONACAT 2015-694159). M.E. acknowledges the European Union’s Horizon 2020 research and innovation programme (Marie Skłodowska-Curie Grant Agreement No. 704098) for the execution of the project related to this article and the Spanish MICINN for the current Ramón y Cajal Contract (No. RYC2018-024396-I). D.Y. acknowledges the financial support of the “CaSh” project through EUR Grant NanoX No. ANR-17-EURE-0009 in the framework of the “Programme des Investissements d’Avenir.”

A synthetic fast-ion loss (FIL) detector and an imaging Heavy Ion Beam Probe (i-HIBP) have been implemented in the 3D hybrid kinetic-magnetohydrodynamic code MEGA. First synthetic measurements from these two diagnostics have been obtained for neutral beam injection-driven Alfvén Eigenmode (AE) simulated with MEGA. The synthetic FILs show a strong correlation with the AE amplitude. This correlation is observed in the phase-space, represented in coordinates (P, E), being toroidal canonical momentum and energy, respectively. FILs and the energy exchange diagrams of the confined population are connected with lines of constant E, a linear combination of E and P. First i-HIBP synthetic signals also have been computed for the simulated AE, showing displacements in the strike line of the order of ∼1 mm, above the expected resolution in the i-HIBP scintillator of ∼100 μm., This work received funding from the European Starting Grant (ERC) from project 3D-FIREFLUC and from the Spanish Ministry of Science under Grant No. FPU19/02267. This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 and 2019-2020 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

An extensive validation effort performed for a modest-beta NSTX NBI-heated H-mode discharge predicts that electron thermal transport can be entirely explained by electron-scale turbulence fluctuations driven by the electron temperature gradient mode (ETG), both in conditions of strong and weak ETG turbulence drive. Thermal power-balance estimates computed by TRANSP as well as the shape of the high-k density fluctuation wavenumber spectrum and the fluctuation level ratio between strongly driven and weakly driven ETG-turbulence conditions can be matched by nonlinear gyrokinetic simulations and a synthetic diagnostic for high-k scattering. Linear gyrokinetic simulations suggest that the ion-scale instability in the weak ETG condition is close to the critical threshold for the kinetic ballooning mode instability, and nonlinear ion-scale gyrokinetic simulations show that turbulence might be in a state reminiscent of a Dimits' shift regime, opening speculation on the role that ion-scale turbulence might play for the weak ETG condition. A simulation that matched all experimental constraints is chosen to project high-k turbulence spectra in NSTX-U, revealing that the new high-k system [R. Barchfeld et al., Rev. Sci. Instrum. 89, 10C114 (2018)] should be sensitive to density fluctuations from radially elongated streamer structures. Two schemes are designed to characterize the radial and poloidal wavenumber dependence of the density fluctuation wavenumber power spectrum around the streamer peak, suggesting future high-k fluctuation measurements could be sensitive to an asymmetry in the kr spectrum introduced due to the presence of strong background flow shear.

We show that new functionality of spin-orbit-active electronic weak links can be achieved by their time-dependent mechanical deformation. As an illustration we use a simple model to calculate the electronic spin current generated by rotating a bent spin-orbit-active nanowire coupled to bulk metallic leads.We show that new functionality of spin-orbit-active electronic weak links can be achieved by their time-dependent mechanical deformation. As an illustration we use a simple model to calculate the electronic spin current generated by rotating a bent spin-orbit-active nanowire coupled to bulk metallic leads.

We theoretically consider a nanomechanical link between two metallic leads subject to a temperature drop. It is shown that mechanical dynamics of such system can be strongly affected by a heat flow through it via the position dependent electron-electron interaction, even though the electronic transport between leads is blocked. In particular, it is demonstrated that, under certain conditions, the stationary distribution of the excitations in the mechanical subsystem has a Boltzmann form with an effective temperature, which is much lower than the temperature of the environment; this seems rather counterintuitive. We also find that a change in the direction of the temperature gradient can result in the generation of mechanical vibrations rather than the heating of the mechanical subsystem.

Bubbly drinks are surprisingly attractive. There is something about the nature of the these beverages that make them preferable among other choices. In this article we explore the physics involved in this particular kind of two-phase, mass-transfer-driven flows., Extended version of Zenit R and Rodr\'iguez-Rodr\'iguez J. The fluid mechanics of bubbly drinks. Physics Today, Vol. 71(11) pp. 44-50, November 2018

This paper provides a review of the compact intense electron-beam accelerators (IEBAs) based on liquid pulse forming lines (PFLs) that have been developed at the National University of Defense Technology (NUDT) in China. The history and roadmap of the compact IEBAs used to drive high-power microwave (HPM) devices at NUDT are reviewed. The properties of both de-ionized water and glycerin as energy storage media are presented. Research into the breakdown properties of liquid dielectrics and the desire to maximize energy storage have resulted in the invention of several coaxial PFLs with different electromagnetic structures, which are detailed in this paper. These high energy density liquid PFLs have been used to increase the performance of IEBA subsystems, based on which the SPARK (Single Pulse Accelerator with spark gaps) and HEART (High Energy-density Accelerator with Repetitive Transformer) series of IEBAs were constructed. This paper also discusses how these compact IEBAs have been used to drive typical HPM devices and concludes by summarizing the associated achievements and the conclusions that can be drawn from the results. Keywords: High-power microwave (HPM), Intense electron-beam accelerator (IEBA), Pulsed power technology (PPT), Pulse forming line (PFL), Fluid of high energy density, De-ionized water, Glycerin, PACS codes: 52.80.Wq, 52.59.Mv, 77.22.Jp, 84.70.+p, 88.60.-m

The ground-state energy of a finite inhomogeneous system of bosons located in a scalar external field was found within the framework of the self-consistent Hartree-Fock approximation, on the basis of the representation of the second quantization without using the formalism of anomalous averages. The ground-state wave function corresponds to the stationary Gross-Pitaevskii equation for the Bose-Einstein condensate wave function. It was shown that the ground-state energy can be found using the energy determined by the stationary Gross-Pitaevskii equation only for a system that satisfies the thermodynamic limit.

This work addresses the numerical modeling of vortex loops in superfluid helium after loop reconnection at various temperatures. Modeling was conducted within the vortex filament method using the full Biot-Savart equation. It was found that the dynamics of vortex loops substantially depend on the initial position of the loops, and that temperature affects the number and size of the formed loops, the amplitude of the Kelvin waves and their decay behavior as well as the velocity of motion of the loops and their separate elements. The time dependence of the distance between the nearest elements of the emergent vortex loop is described by the power law, with the power of 1/2 before and after reconnection.

The visualization of phenomena on the surface of superfluid He II by means of light glass tracers located in a thin layer below the surface of the fluid has made it possible to observe, for the first time, the appearance of a vortex flow and two-dimensional macroscopic vortices that are formed on the surface of the superfluid in a vibrating cell as a result of nonlinear interaction between noncollinear Faraday waves. Standing Faraday waves are excited on the He II surface with vertical oscillations of the cell with relative variable acceleration above the threshold of the parametric instability β > βc ≈ 0.04. It was found that during intense wave-pumping at a frequency of 40 Hz with prolonged exposure for ∼270 seconds, the dependence of the kinetic energy of a vortex system on the wave vector E(k) at k ≥ 4.5 cm–1 can be described as a power law of the form E(k) ∼ k–3. In other words, with time, both an inverse turbulent cascade and a direct one may arise in a system of macroscopic vortices generated by waves on the surface of an He II layer with a depth of ∼0.4 cm.The visualization of phenomena on the surface of superfluid He II by means of light glass tracers located in a thin layer below the surface of the fluid has made it possible to observe, for the first time, the appearance of a vortex flow and two-dimensional macroscopic vortices that are formed on the surface of the superfluid in a vibrating cell as a result of nonlinear interaction between noncollinear Faraday waves. Standing Faraday waves are excited on the He II surface with vertical oscillations of the cell with relative variable acceleration above the threshold of the parametric instability β > βc ≈ 0.04. It was found that during intense wave-pumping at a frequency of 40 Hz with prolonged exposure for ∼270 seconds, the dependence of the kinetic energy of a vortex system on the wave vector E(k) at k ≥ 4.5 cm–1 can be described as a power law of the form E(k) ∼ k–3. In other words, with time, both an inverse turbulent cascade and a direct one may arise in a system of macroscopic vortices generated by wa...

The paper analyzes an approach to the generalization of the conventional Bose–Einstein statistics based on the nonadditive entropy of Tsallis. A detailed derivation of thermodynamic functions is presented. The calculations are made for the specific heat of two model systems, namely, the ideal three-dimensional gas obeying the nonadditive modification of the Bose–Einstein statistics and the system with linear excitation spectrum attempted as a qualitative approximation of liquid ⁴He thermodynamics. Проаналізовано підхід до узагальнення традиційної статистики Бозе–Ейнштейна на основі неадитивної ентропії Цалліса. Подано докладне виведення термодинамічних функцій. Зроблено розрахунки для питомої теплоємності двох модельних систем, а саме: ідеального тривимірного газу, що підкоряється неаддитивній модифікації статистики Бозе–Ейнштейна, та системи з лінійним спектром елементарних збуджень, прийнятої за якісне наближення термодинаміки рідкого ⁴He. Проанализирован подход к обобщению традициионной статистики Бозе–Эйнштейна на основе неаддитивной энтропии Цаллиса. Представлен подробный вывод термодинамических функций. Сделаны расчеты для удельной теплоемкости двух модельных систем, а именно: идеального трехмерного газа, подчиняющегося неаддитивной модификации статистики Бозе–Эйнштейна, и системы с линейным спектром элементарных возбуждений, принятой как качественное приближение термодинамики жидкого ⁴He.

A microscopic approach for the construction of the kinetic theory of low-temperature hydrogen-like gases in an external electromagnetic field was developed. The approach is based on the formulation of secondary quantization in the presence of bound states of particles. It is suggested that the bound state (for example, a hydrogen-like atom of alkali metal) is formed by two charged fermions of different sorts — the valence electron and the ion core. The reduced description of relaxation processes establishes the basis for the formulation of the kinetic equations. Within the developed theoretical framework, the system of kinetic equations for Wigner’s distribution functions of free fermions of both sorts and their bound states, hydrogen-like atoms, is developed accounting for an external and self-consistent (intermediate) fields acting on the system. The obtained equations of motion for Wigner’s distribution functions serve as a basis for analyzing non-equilibrium effects and phenomena related to the influe...

The solvation of impurity atoms {Na, K, Rb, Cs, Mg, Ca, Sr, Ba} with small ionization energy in liquid helium is studied. It is shown that allowance for unmatched interaction of impurity atoms and helium atoms is important for determining the parameters of the atomic state. The size of the bubble state R0 is determined by the strong repulsion between helium atoms and valence electrons of impurity atoms. The R0 value is universal, and the expression 2R0/ν = const ≈ 11–13 depends weakly on the place of the impurity atom in the periodic table. The parameter ν is given by the impurity ionization energy J = 1/2ν2 (in atomic units); the ν value indicates the size of the impurity atom. An energy barrier that separates the bulk and surface atomic impurity states is determined.The solvation of impurity atoms {Na, K, Rb, Cs, Mg, Ca, Sr, Ba} with small ionization energy in liquid helium is studied. It is shown that allowance for unmatched interaction of impurity atoms and helium atoms is important for determining the parameters of the atomic state. The size of the bubble state R0 is determined by the strong repulsion between helium atoms and valence electrons of impurity atoms. The R0 value is universal, and the expression 2R0/ν = const ≈ 11–13 depends weakly on the place of the impurity atom in the periodic table. The parameter ν is given by the impurity ionization energy J = 1/2ν2 (in atomic units); the ν value indicates the size of the impurity atom. An energy barrier that separates the bulk and surface atomic impurity states is determined.

I thank Silvana Cardoso and John Davidson (1926–2019) for many interesting discussions in the tea room of the Department of Chemical Engineering and Biotechnology in Cambridge over the years that have contributed to this review, ranging from the fluid mechanics of explosions, to the lessons of Flixborough for the education of engineers, to how Tom Bacon developed, first at C. A. Parsons in Newcastle and then in that Department, the hydrogen–oxygen fuel cell used by NASA in the Apollo program. I acknowledge the financial support of the Spanish MINCINN Project, No. FIS2016-77692-C2-2-P., Gas and vapor explosions have been involved in industrial accidents since the beginnings of industry. A century ago, at 11:55 am on Friday September 24, 1920, the petroleum barge Warwick exploded in London’s docklands and seven men were killed. Understanding what happened when it blew up as it was being refurbished, and how to prevent similar explosions, involves fluid mechanics and thermodynamics plus chemistry. I recount the 1920 accident as an example, together with the history of thermo-kinetic explosions prior to 1920 and up to the present day, and I review the history and the actual state of the science of explosion and the roles of fluid mechanics, thermodynamics, and chemistry in that science. The science of explosions has been aware of its societal implications from the beginning, but, despite advances in health and safety over the past century, is there still work to do?, Spanish MINCINN Project, No. FIS2016-77692-C2-2-P.

This work addresses the problem of pattern analysis in networks consisting of delay-coupled identical Lur'e systems. We study a class of nonlinear systems, which, being isolated, are globally asymptotically stable. Assembling such systems into a network via time-delayed coupling may result in the change of network equilibrium stability under parameter variation in the coupling. In this work, we focus on cases where a Hopf bifurcation causes the change of stability of the network equilibrium and leads to the occurrence of oscillatory modes (patterns). Moreover, some of these patterns can co-exist for the same set of coupling parameters, which makes the analysis by means of common methods, such as the Lyapunov-Krasovskii method or the analysis of Poincaré maps, cumbersome. A numerically efficient algorithm, aiming at the computation of the oscillatory patterns occurring in such networks, is presented. Moreover, we show that our approach is able to deal with co-existing patterns, and both stable and unstable regimes can be simultaneously computed, which gives deep insight into the network dynamics. In order to illustrate the efficiency of the method, we present two examples in which the instability of the network equilibria is caused by a subcritical and a supercritical Hopf bifurcation. In addition, a bifurcation analysis of the subcritical case is performed in order to further explain the occurrence of the detected coexisting modes. ispartof: Chaos vol:31 issue:3 ispartof: location:United States status: Published online

High-flux synchrotron radiation has been employed in a time-resolved manner to characterize the distinct topology features and dynamics of different cavitation regimes arising in a throttle orifice with an abrupt flow-entry contraction. Radiographs obtained though both x-ray phase-contrast and absorption imaging have been captured at 67 890 frames per second. The flow lies in the turbulent regime (Re = 35 500), while moderate (CN = 2.0) to well-established (CN = 6.0) cavitation conditions were examined encompassing the cloud and vortical cavitation regimes with pertinent transient features, such as cloud-cavity shedding. X-ray phase-contrast imaging, exploiting the shift in the x-ray wave phase during interactions with matter, offers sharp-refractive index gradients in the interface region. Hence, it is suitable for capturing fine morphological fluctuations of transient cavitation structures. Nevertheless, the technique cannot provide information on the quantity of vapor within the orifice. Such data have been obtained utilizing absorption imaging, where beam attenuation is not associated with scattering and refraction events, and hence can be explicitly correlated with the projected vapor thickness in line-of-sight measurements. A combination of the two methods is proposed as it has been found that it is capable of quantifying the vapor content arising in the complex nozzle flow while also faithfully illustrating the dynamics of the highly transient cavitation features.

A new method to determine the arbitrary electron energy distribution function (EEDF) from the optical emission spectroscopic measurement in atmospheric-pressure plasma is introduced. The optical emission spectroscopy (OES) continuum emission spectrum, dominated by electron-neutral bremsstrahlung radiation, is analyzed to inspect the usefulness of the conventional OES measurement range for EEDF determination. The EEDF is reconstructed from the OES continuum radiation spectrum by applying machine learning to solve the bremsstrahlung emissivity equation inversely. Through iterative statistical analysis, the presented genetic algorithm can locate the EEDF reliably. Verification of the algorithm shows that theoretical Maxwellian and Druyvesteynian EEDFs can be partially reconstructed from a realistic OES measurement range. Furthermore, preliminary experimental EEDF results of an argon dielectric barrier discharge (DBD) OES measurement are given. The electron energy range and resolution of the determined EEDF are discussed. The results in this paper show potential for accurate determination of the arbitrary EEDF in atmospheric-pressure plasma using simple OES equipment.

Although producing clusters by physical methods offers many benefits, low deposition rates have prevented cluster beam deposition techniques from being adopted more widely. The influence of the gas aerodynamics inside the condensation chamber of a magnetron cluster source on the cluster throughput is reported, leading to an improved understanding of the gas aerodynamics’ influence on cluster transport. In the first part of the paper the influence of the carrier gas’ inlet position on the cluster flux is studied. In particular, two inlet configurations were investigated, i.e. from the rear of the chamber and from within the magnetron sputtering source. It was found experimentally that the latter configuration can lead to an increased cluster flux, under the same conditions of gas pressure and power applied to the magnetron. This behaviour is explained with the help of simulations. In the second part of the paper, the gas dynamics behaviour inside four chamber shapes, namely two cylindrical shapes with different cross-section diameters and two conical shapes with different apex angles, was simulated. The modelling showed that the fraction of clusters successfully leaving the aggregation zone can be increased by up to 8 times from the worst to the best performing chamber geometries studied. Finally, the cluster throughput was determined experimentally using a quartz microbalance in two of the four chamber designs. It was found that the cluster flux increased up to one order of magnitude, reaching ~ 20 mg per hour for a condensation chamber with a smaller cross section and a conical exit. ispartof: Review Of Scientific Instruments vol:92 issue:3 ispartof: location:United States status: Published online

A hanging pendulum thrust balance has been developed by Imperial College London in collaboration with the European Space Agency (ESA) to characterize a wide range of static fire electric propulsion and chemical micro-propulsion devices with thrust in the range of 1 mN to 1 N. The thrusters under investigation are mounted on a pendulum platform, which is suspended from the support structure using stainless steel flexures. The displacement of the platform is measured using an optical laser triangulation sensor. Thermal stability is ensured by a closed loop self-compensating heating system. The traceability and stability of the calibration are ensured using two separate calibration subsystems: a voice coil actuator and a servomotor pulley system. Two nearly identical thrust balances have been constructed, with one being tested in the Imperial Plasma Propulsion Laboratory and the other in the ESA Propulsion Laboratory. Both balances show a high degree of linearity in the range of 0.5 mN-100 mN. Both instruments have demonstrated a stable calibration over several days, with an estimated standard deviation on thrust measurements better than 0.27 mN for low thrust measurements. The same electric propulsion test article was used during both tests: a Quad Confinement Thruster (QCT) variant called QCT Phoenix. This thruster differed from previous QCT designs by having a newly optimized magnetic topology. The device produced thrust up to 2.21 ± 0.22 mN with a maximum specific impulse of 274 ± 41 s for an anode power range of 50 W-115 W.

Turbulent partially filled pipe flow was investigated using stereoscopic particle imaging velocimetry in the cross-stream plane for a range of flow depths at a nominally constant Reynolds number of 30 000 (based on the bulk velocity and hydraulic diameter). Unlike full pipe flow, which is axisymmetric, the turbulent kinetic energy exhibits significant azimuthal (and radial) variation. Proper orthogonal decomposition (POD) of the fluctuating velocity field indicates that the leading-order POD modes occupy the “corners” where the free surface meets the pipe wall and that these modes, which are closely linked to the instantaneous cellular structure, contribute nearly a quarter of the overall turbulent kinetic energy. Spatial distributions of the large- and very-large-scale motions (LSMs/VLSMs) estimated from pseudo-instantaneous three-dimensional velocity fields reveal a preference for the sides (in close proximity to the free surface) and bottom quadrant of the pipe. That the LSMs and VLSMs are shown to populate a region spanning the width of the free surface, as well as the corners, strongly suggests that there is a dynamical connection between LSMs/VLSMs and the instantaneous cellular structures in turbulent partially filled pipe flow, which can explain the spatial redistribution of the turbulent kinetic energy.

Historically, rational choice theory has focused on the utility maximization principle to describe how individuals make choices. In reality, there is a computational cost related to exploring the universe of available choices and it is often not clear whether we are truly maximizing an underlying utility function. In particular, memory effects and habit formation may dominate over utility maximisation. We propose a stylized model with a history-dependent utility function where the utility associated to each choice is increased when that choice has been made in the past, with a certain decaying memory kernel. We show that self-reinforcing effects can cause the agent to get stuck with a choice by sheer force of habit. We discuss the special nature of the transition between free exploration of the space of choice and self-trapping. We find in particular that the trapping time distribution is precisely a Zipf law at the transition, and that the self-trapped phase exhibits super-aging behaviour., 7 pages, 4 figures, 1 table

An Imaging Neutral Particle Analyzer (INPA) diagnostic has been designed for the ASDEX Upgrade (AUG) tokamak. The AUG INPA diagnostic will measure fast neutrals escaping the plasma after charge exchange reactions. The neutrals will be ionized by a 20 nm carbon foil and deflected toward a scintillator by the local magnetic field. The use of a neutral beam injector (NBI) as an active source of neutrals will provide radially resolved measurements, while the use of a scintillator as an active component will allow us to cover the whole plasma along the NBI line with unprecedented phase-space resolution (, This project received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 805162) and the Spanish Ministerio de Ciencia, Innovación y Universidades (Grant No. FPU19/02486).

Sloshing in a sea cage with a slowly rotating liquid is investigated. The cage is axisymmetric, and the liquid is subjected to a nearly uniform angular velocity about the vertical axis of the cage. Both experimental and theoretical investigations are presented. It is shown that rotation modifies the sloshing regimes of a non-rotating liquid by splitting the natural frequencies. Therefore, resonant sloshing regimes can be manipulated by varying the rotation rate of the liquid. This is the authors’ accepted and refereed manuscript to the article. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in (citation of published article) and may be found at http://dx.doi.org/10.1063/5.0037408

Airborne respiratory diseases such as SARS-CoV-2 (COVID-19) pose significant challenges for public transportation. Several recent outbreaks of SARS-CoV-2 indicate the high risk of transmission among passengers on public buses if special precautions are not taken. This study presents a combined experimental and numerical analysis to identify transmission mechanisms on an urban bus and assess strategies to reduce risk. The effects of the ventilation and air-conditioning systems, opening windows and doors, and wearing masks are analyzed. Specific attention is made to the transport of sub-micron and micron-size particles relevant to typical respiratory droplets. High-resolution instrumentation was used to measure size distribution and aerosol response time on a University of Michigan campus bus under these different conditions. Computational fluid dynamics was employed to measure the airflow within the bus and evaluate risk. A risk metric was adopted based on the number of particles exposed to susceptible passengers. The flow that carries these aerosols is predominantly controlled by the ventilation system, which acts to uniformly distribute the aerosol concentration throughout the bus while simultaneously diluting it with fresh air. The opening of doors and windows was found to reduce the concentration by approximately one half, albeit its benefit does not uniformly impact all passengers on the bus due to recirculation of airflow caused by entrainment through windows. Finally, it was found that well fitted surgical masks, when worn by both infected and susceptible passengers, can nearly eliminate the transmission of the disease., 22 pages, 15 figures

For current and future large scale tokamaks, neutral beams for heating and current drive are generated from the neutralisation of large negative ion beams with energies up to 1 MeV and current of up to 40 A. To improve efficiency and prevent high heat loads on beamline components, permanent magnets are used to deflect co-extracted electrons out of the beam at a low energy. This field also affects the negative ions as they are accelerated, causing beamlets to exit the grid system with a residual offset and deflection angle. This adversely affects the overall divergence of the beam, and compensation is foreseen in future devices. Measurements of the residual deflection of a single beamlet have been carried out at the BATMAN Upgrade test facility by calculating relative beamlet angles from beam emission spectroscopy (BES) spectra, and through the use of one-dimensional carbon fibre composite (1D-CFC) tile calorimetry to find beamlet positions. It is described how these measurements can be made, and that they are limited to relative measurements only, for a single beamlet and for a single line of sight. The amount of beamlet deflection is shown to change significantly, by up to 0.6°(10 mrad), depending on the operational parameters used. As is to be expected the beamlet deflection angle is observed to be affected by changes to the voltages of the acceleration system. However, the beamlet deflection angle is also observed to change with RF power and other source parameters, which, to a first approximation, should only affect beamlet divergence, and not the deflection. These changes to beamlet deflection through parameters other than the grid voltages used may have consequences for systems planning to use suppression systems for the zig-zag deflection. The effectiveness of the suppression system may be reduced due to changes in the source parameters, which could lead to beam losses and high heat loads on downstream components.

Jet fans are increasingly preferred over traditional ducted systems as a means of ventilating pollutants in large environments such as underground car parks. The spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)—which causes the novel coronavirus disease—through the jet fans in underground car parks has been considered a matter of key concern. A quantitative understanding of the propagation of respiratory droplets/particles/aerosols containing the virus is important. However, to date, studies have yet to demonstrate viral (e.g., SARS-CoV-2) transmission in underground car parks equipped with jet fans. In this paper, numerical simulation has been performed to assess the effects of jet fans on the spreading of viruses inside underground car parks.

Clinic encounters of dentists and otolaryngologists inherently expose these specialists to an enhanced risk of severe acute respiratory syndrome coronavirus 2 infection, thus threatening them, their patients, and their practices. In this study, we propose and simulate a helmet design that could be used by patients to minimize the transmission risk by retaining droplets created through coughing. The helmet has a port for accessing the mouth and nose and another port connected to a vacuum source to prevent droplets from exiting through the access port and contaminating the environment or clinical practitioners. We used computational fluid dynamics in conjunction with Lagrangian point-particle tracking to simulate droplet trajectories when a patient coughs while using this device. A range of droplet diameters and different operating conditions were simulated. The results show that 100% of the airborne droplets and 99.6% of all cough droplets are retained by the helmet.

openaire: EC/H2020/862644/EU//QUARTET Quantum control methods for three-level systems have become recently an important direction of research in quantum information science and technology. Here we present numerical simulations using realistic experimental parameters for quantum process tomography in STIRAP (stimulated Raman adiabatic passage) and saSTIRAP (superadiabatic STIRAP). Specifically, we identify a suitable basis in the operator space as the identity operator together with the 8 Gell-Mann operators, and we calculate the corresponding process matrices, which have 9 × 9=81 elements. We discuss these results for the ideal decoherence-free case, as well as for the experimentally-relevant case with decoherence included.

In this work, the flow over an elliptic cylinder near a moving wall is investigated for Reynolds numbers less than 150. Here, the ratio between the gap (i.e., the distance between the cylinder and the wall) and the length of the semi-major axis of the elliptic cylinder varies from 0.1 to 5. This ratio is hereafter denoted as the gap ratio. The resulting Kármán vortex street, the two-layered wake, and the secondary vortex street have been investigated and visualized. Numerical simulations show that for the steady flow, the wake is composed of two asymmetric recirculation vortices, while a decrease in the gap ratio suppresses the vortex shed from the lower part of the cylinder. For the unsteady flow, the wake can be classified into four different patterns based on the wake structures (the Kármán vortex street, the two-layered wake, and the secondary vortex street). The regions of these wake patterns are given in the gap ratio and Reynolds number space, showing that the critical Reynolds number for the transition between different patterns increases as the gap ratio decreases. An overall increase in the mean drag coefficient with increasing gap ratios is observed, except for a sudden drop that occurs within a small gap ratio range. Moreover, as the gap ratio increases, the onset location of the two-layered wake first decreases due to a decrease in flow velocity in the gap and then increases due to the weakening of the wall suppression effect. This is the authors’ accepted and refereed manuscript to the article. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in (citation of published article) and may be found at (URL/link for published article abstract).

The averaging principle for Caputo fractional stochastic differential equations has recently attracted much attention. In this paper, we investigate the averaging principle for a type of Caputo fractional stochastic differential equation. Comparing with the existing literature, we shall use different estimate methods to investigate the averaging principle, which will enrich the development of theory for Caputo fractional stochastic differential equations.

A local study of linear electrostatic modes, applicable to the dynamics perpendicular to the magnetic field in a plasma with crossed electric and magnetic fields, is presented. The analysis is based on a two-fluid model that takes into account the finite-electron-gyroradius effects through a rigorous gyroviscosity tensor and includes a dissipative friction force in the electron momentum equation. A comprehensive dispersion relation, valid for arbitrary electron temperature, is derived, which describes properly all the relevant waves for wavelengths longer than the electron Larmor radius. For a homogeneous and dissipationless plasma, such a fluid dispersion relation agrees with the long-wavelength limit of the kinetic electron–cyclotron-drift instability dispersion relation that extends the results to arbitrary short wavelengths. The general fluid dispersion relation covers different parametric regimes that depend on the relative ion-to-electron drift velocity and on the presence of equilibrium inhomogeneities and/or dissipation. Depending on such conditions, its roots yield as follows: two-stream instabilities, driven solely by the relative drift between species; drift-gradient instabilities, driven by the combination of the relative drift and equilibrium gradients; and drift-dissipative instabilities, driven by the combination of the relative drift and friction. Instability thresholds are determined and some distinctive unstable modes are described analytically. This research was funded mainly by the Comunidad de Madrid (Spain), under PROMETEO-CM project, with Grant No. Y2018/NMT-4750. Enrique Bello-Benítez is supported by Spain's Ministerio de Ciencia, Innovación y Universidades, under Grant No. FPU18/03686. Jesús Ramos and Eduardo Ahedo acknowledge support by the ESPEOS project, funded by the Agencia Estatal de Investigación (Spain's National Research and Development Plan), under Grant No. PID2019-108034 RB-I00/AEI/10.13039/501100011033.

We analyze daily time series of stocks of S&P 500 to identify the financial states of US market from 1998 - 2012. The planar maximally filtered graph is constructed from correlation between companies. We measure the hierarchy of the financial graphs using hierarchical path. It is found that the networks are less hierarchical in the beginning of the crises and enhances with crises in the time period. Finally, graph alteration is measured by our propose method and also Jaccard index. We found that the big change of hierarchy altered the network structure. To observe the network variation, our approach gives better result than Jaccard index does.

The heat exchanger system is one of the important components for many of the non-conventional power-producing system. These heat exchanger systems may be used effectively as absorbing and storing heat from say solar ducts/panels, exchanging the heat for solar assisted refrigeration systems, etc. However, developing a compact and high effective heat exchanger system is a challenge. It has also been seen that the heat transfer will be more for the turbulent flows or flows where mixing dominates with higher heat transfer coefficient values. In this paper, we have developed a small concentric annulus heat exchanger having a helical flow passage. This compact heat exchanger is utilized to replace the electric heat source supplied to the Electrolux refrigerator. The helical flow is produced by providing a helical metal baffle between the two concentric annulus pipes. The working medium through the helixchanger is nanoparticle blended with water. CuO and Al2 O3 are the two popularly nanomaterials are mixed with water and their effectiveness is compared. The discrete phase model (DPM) based numerical simulation of the three-dimensional flow through helixchangers is presented here. The DPM exactly mimics the actual flow scenarios where nanoparticles are injected/blended along with the flowing fluid and expected to provide a realistic solution. The flow-through helixchanger is simulated for various Reynolds numbers and corresponding pressure drop, the average heat transfer coefficient is studied and presented here. Due to added nanomaterial in the working medium, the heat transfer is found to be increased by 25-30% as compared to without nanomaterial blend. Also, there are negligible pressure changes hence indicating the same pump power requirements for pumping. At the last, the results are validated with experimental values and their matching is found good.

The development of a novel on-demand droplet generator is reported in this paper based on off-the-shelf electromechanical components. With the ability to produce a broad range of droplet sizes, this device was designed to have minimum components without compromising reliability. The generator performance was assessed by producing water droplets for fire dynamics and suppression studies. Droplet formation at the tip of the nozzle was visualized using high-speed imaging. Stable and unstable regions can be identified easily through the images. Interchangeable nozzles can be used, allowing different droplet sizes. The setting parameters of the device allow accurate control of droplet size and initial speed. The device controls the liquid pressure actively and precisely. The active control of pressure and the ability to have specific droplet ejection parameters ensured the repeatability of droplet conditions. Characterization of the device is presented along with the calibration data, which can be collected in an efficient methodology. These data enable the selection of droplet size and speed when required. This system could easily be implemented in other research areas. Hence, the intention is to share and highlight the generator features for its use in a range of other scientific applications.

Waves in bi-ion plasmas are a ected by asymmetry. The kinetic theory of the Maxwellian and Lorentzian/Kappa-distributed bi-ion plasma is ameliorated to incorporate the transfer of orbital angular momentum from the helical electric eld to the plasma modes. By operating the Laguerre-Gaussian (LG) function, the perturbed distribution function and helical electric eld are decomposed into characteristic axial and azimuthal components. In symmetric bi-ion plasmas, the conventional ion modes/waves are only present if both ions have similar masses and the concentration of the electrons is negligible. An imbalance of the symmetry is considered by the contamination of a small fraction of the heavy immobile ions, which urges the negative ions to become heavier than the positive ions in the bi-ion plasma system. The distinct masses of the positive and negative ions provoke mass-asymmetry in the Kappa-distributed bi-ion plasmas. The signa- ture of the unique acoustic-laden twisted modes in non-Maxwellian asymmetric bi-ion plasma is perceived by the temperature of the lighter positive ions and the dynamics of the heavier negative ion. The deliberated results of Landau damping are displayed for distinct values of the azimuthal wave-number and spectral index, temperature-variation and mass-asymmetry. ispartof: Physics Of Plasmas vol:27 issue:12 status: published

The drying behavior of coatings is essential for the development of formulations in order to obtain reliable and defect free finishes. There are two major measures of interest: the development of the stress responsible for cracking and the drying rate that gives insight into the morphological structure. The cantilever deflection method is the predominant way of determining stresses under defined drying conditions such as temperature and humidity. However, both measures of interest are currently obtained using two different coatings when dried in a chamber or a single coating with simultaneous measurements that can only be dried under ambient conditions. In this paper, we present an apparatus design based on the cantilever deflection method that allows simultaneous measurement of the stress and drying rate in an environmentally controlled chamber. ispartof: Review of Scientific Instruments vol:91 issue:12 ispartof: location:United States status: published

Coronavirus disease 2019 (COVID-19) has become a global pandemic infectious respiratory disease with high mortality and infectiousness. This paper investigates respiratory droplet transmission, which is critical to understanding, modeling and controlling epidemics. In the present work, we implemented flow visualization, particle image velocimetry (PIV) and particle shadow tracking velocimetry (PSTV) to measure the velocity of the airflow and droplets involved in coughing and then constructed a physical model considering the evaporation effect to predict the motion of droplets under different weather conditions. The experimental results indicate that the convection velocity of cough airflow presents the relationship $t^{-0.7}$ with time; hence, the distance from the cougher increases by $t^{0.3}$ in the range of our measurement domain. Substituting these experimental results into the physical model reveals that the small droplets (initial diameter $D \leq$ 100 $\mu$m) evaporate to droplet nuclei and that the large droplets with $D \geq$ 500 $\mu$m and initial velocity $u_0 \geq$ 5 m/s travel more than 2 m. Winter conditions of low temperature and high relative humidity can cause more droplets to settle to the ground, which may be a possible driver of a second pandemic wave in the autumn and winter seasons., Comment: 27 pages, 15 figures, COVID-19, article

Identifying the relative importance of the different transmission routes of the SARS-CoV-2 virus is an urgent research priority. To that end, the different transmission routes and their role in determining the evolution of the Covid-19 pandemic are analyzed in this work. The probability of infection caused by inhaling virus-laden droplets (initial ejection diameters between 0.5 µm and 750 µm, therefore including both airborne and ballistic droplets) and the corresponding desiccated nuclei that mostly encapsulate the virions post droplet evaporation are individually calculated. At typical, air-conditioned yet quiescent indoor space, for average viral loading, cough droplets of initial diameter between 10 µm and 50 µm are found to have the highest infection probability. However, by the time they are inhaled, the diameters reduce to about 1/6th of their initial diameters. While the initially near unity infection probability due to droplets rapidly decays within the first 25 s, the small yet persistent infection probability of desiccated nuclei decays appreciably only by O(1000s) , assuming that the virus sustains equally well within the dried droplet nuclei as in the droplets. Combined with molecular collision theory adapted to calculate the frequency of contact between the susceptible population and the droplet/nuclei cloud, infection rate constants are derived ab initio, leading to a susceptible-exposed-infectious-recovered-deceased model applicable for any respiratory event-vector combination. The viral load, minimum infectious dose, sensitivity of the virus half-life to the phase of its vector, and dilution of the respiratory jet/puff by the entraining air are shown to mechanistically determine specific physical modes of transmission and variation in the basic reproduction number R0 from first-principles calculations.

The coronavirus disease 2019 (COVID-19) outbreak, due to SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), originated in Wuhan, China and is now a global pandemic. The unavailability of vaccines, delays in diagnosis of the disease, and lack of proper treatment resources are the leading causes of the rapid spread of COVID-19. The world is now facing a rapid loss of human lives and socioeconomic status. As a mathematical model can provide some real pictures of the disease spread, enabling better prevention measures. In this study, we propose and analyze a mathematical model to describe the COVID-19 pandemic. We have derived the threshold parameter basic reproduction number, and a detailed sensitivity analysis of this most crucial threshold parameter has been performed to determine the most sensitive indices. Finally, the model is applied to describe COVID-19 scenarios in India, the second-largest populated country in the world, and some of its vulnerable states. We also have short-term forecasting of COVID-19, and we have observed that controlling only one model parameter can significantly reduce the disease's vulnerability.

Recent studies have indicated that COVID-19 is an airborne disease, which has driven conservative social distancing and widescale usage of face coverings. Airborne virus transmission occurs through droplets formed during respiratory events (breathing, speaking, coughing, and sneezing) associated with the airflow through a network of nasal and buccal passages. The airflow interacts with saliva/mucus films where droplets are formed and dispersed, creating a route to transmit SARS-CoV-2. Here, we present a series of numerical simulations to investigate droplet dispersion from a sneeze while varying a series of human physiological factors that can be associated with illness, anatomy, stress condition, and sex of an individual. The model measures the transmission risk utilizing an approximated upper respiratory tract geometry for the following variations: (1) the effect of saliva properties and (2) the effect of geometric features within the buccal/nasal passages. These effects relate to natural human physiological responses to illness, stress, and sex of the host as well as features relating to poor dental health. The results find that the resulting exposure levels are highly dependent on the fluid dynamics that can vary depending on several human factors. For example, a sneeze without flow in the nasal passage (consistent with congestion) yields a 300% rise in the droplet content at 1.83 m (≈6 ft) and an increase over 60% on the spray distance 5 s after the sneeze. Alternatively, when the viscosity of the saliva is increased (consistent with the human response to illness), the number of droplets is both fewer and larger, which leads to an estimated 47% reduction in the transmission risk. These findings yield novel insight into variability in the exposure distance and indicate how physiological factors affect transmissibility rates. Such factors may partly relate to how the immune system of a human has evolved to prevent transmission or be an underlying factor driving superspreading events in the COVID-19 pandemic.

The infection risks of Biden, Wallace, and the audience by Trump and the first lady were assessed during the first presidential debate. The debate scene was established numerically, and two cases, i.e., only Trump being infected and both Trump and the first lady being infected, were set up for risk analysis. The infection probabilities at different positions were assessed by using the Wells-Riley equation with consideration of the effects of air distribution and face mask. It was concluded that (1) the infection risks of Biden and Wallace were lower due to the reasonable distance from Trump, with the maximum probability of 0.34% at 40 quanta/h for both Trump and the first lady being infected; (2) the infection probabilities in the audience area were lower for the long distance from the debate stage, with the maximum probability of 0.35%. Wearing masks resulted in a notable decrease in the infection probability to 0.09%; and (3) there was a certain local area surrounding Trump and the first lady with a relatively greater infection probability. The preliminary analysis provides some reference for protection of the next presidential debate and other public events.

The indirect drive approach to inertial confinement fusion (ICF) has undergone important advances in the past years. The improvements in temperature and density diagnostic methods are leading to more accurate measurements of the plasma conditions inside the hohlraum and therefore to more efficient experimental designs. The implementation of dot spectroscopy has proven to be a versatile approach to extracting spaceand time-dependent electron temperatures. In this method a microdot of a mid-Z material is placed inside the hohlraum and its K-shell emission spectrum is used to determine the plasma temperature. However, radiation transport of optically thick lines acting within the cylindrical dot geometry influences the outgoing spectral distribution in a manner that depends on the viewing angle. This angular dependence has recently been studied in the high energy density (HED) regime at the OMEGA laser facility, which allowed us to design and benchmark appropriate radiative transfer models that can replicate these geometric effects. By combining these models with the measurements from the dot spectroscopy experiments at the National Ignition Facility (NIF), we demonstrate here a novel technique that exploits the transport effects to obtain time-resolved measurements of the ion density of the tracer dots, without the need for additional diagnostics. We find excellent agreement between experiment and simulation, opening the possibility of using these geometric effects as a density diagnostic in future experiments.

Recently there have been significant theoretical advances in our understanding of liquids and dense supercritical fluids based on their ability to support high frequency transverse (shear) waves. Here, we have constructed a new computer model using these recent theoretical findings (the phonon theory of liquid thermodynamics), to model liquid internal energy across a wide pressure-temperature range. We have applied it to a number of real liquids in both the subcritical regime and the supercritical regime, in which the liquid state is demarcated by the Frenkel line. Our fitting to experimental data in a wide pressure-temperature range has allowed us to test the new theoretical model with hitherto unprecedented rigour. We have quantified the degree to which the prediction of internal energy and heat capacity is constrained by the different input parameters: The liquid relaxation time (initially obtained from the viscosity), the Debye wavenumber and the infinite-frequency shear modulus. The model is successfully applied to output the internal energy and heat capacity data for several different fluids (Ar, Ne, $N_2$, Kr) over a range of densities and temperatures. We find that the predicted heat capacities are extremely sensitive to the values used for the liquid relaxation time. If these are calculated directly from the viscosity data then, in some cases, changes within the margins of experimental error in the viscosity data can cause the heat capacity to exhibit a completely different trend as a function of temperature. Our code is computationally inexpensive, and it is available for other researchers to use., Comment: The following article has been accepted by Physics of Fluids, and published at https://doi.org/10.1063/5.0025871

In this theoretical study, we use linear stability analysis to investigate the cause of parietal vortex shedding in Taylor–Culick flow, which is representative of the flow in solid rocket motors. We focus on the effects of the lateral-injection Reynolds number and the length-to-radius ratio of the combustion chamber. Through a comparison with pipe flow, we find that flow turning is a major contributor to parietal vortex shedding. We explore the role of amphidromic points and find that they can divide the flow field into two distinct regions, an outer region with strong perturbations and an inner region with weak perturbations. In the outer region, we find that the velocity perturbations develop advection patterns with axial (streamwise) periodicity, while the pressure perturbations induce flow gradients that enhance shear stresses. Collectively, these effects are thought to combine to induce parietal vortex shedding in solid rocket motors.

Mass transport of the Knudsen gas in a porous medium is investigated on the basis of the kinetic theory of gases. First, the mass flow conductance is computed numerically for various porosities and solid grain sizes by stochastic particle simulations (SPS). Then, a kinetic model with a homogeneous scatterer is introduced, which contains the reference Knudsen number as the sole parameter that characterizes the collision frequency of gas molecules with the micro-structural solid surface. With the aid of the standard asymptotic analyses for small and large Knudsen numbers combined with the percolation theory, the effective reference Knudsen number is identified to reproduce the SPS results for a wide range of porosities., This paper is part of the Special Topic, Advances in Micro/Nano Fluid Flows: In Memory of Prof. Jason Reese.