bluuebunny/crossref_metadata_2025 huggingface dataset:
The moral economy of the great resignation
Authors: Varavallo Giuseppe , Scarpetti Giulia , Barbera Filippo
Published: September 2023

The “Great Resignation” or “The Big Quit” represents a significant shift in people’s importance of employment. In September 2021, U.S. Department of Labor data revealed that 4.4 million Americans quit their jobs, an increase of over 1.13 million from September 2020. This study aims to explore the socio-psychological reasons behind the Great Resignation and potential future shifts in how people view work in their lives. A data collection of 955 highly rated posts from the r/antiwork subreddit was analyzed using the BERTopic method to semantically examine the posts into identifiable topics from February 2020 to February 2022. Subsequently, the moral economy framework was used to investigate these topics, classifying the reasons into three dimensions: ‘Work and Employment,’ which reflects organizational factors, ‘Social Justice and Activism,’ which includes community-level considerations, and ‘Health, Well-being, and Lifestyle,’ which relates to individual circumstances. The study reveals a ‘vocabulary of motives,’ including flexibility, meaningful work, social responsibility, and self-care, showcasing the interconnectedness across individual, community, and organizational dimensions. This evidence suggests an ongoing significant transformation in societal importance and understanding of work. These findings shed light on the profound shift in work values, contributing to a more comprehensive understanding of the Great Resignation phenomenon, and have far-reaching implications for organizations and policymakers.
Contingent reward versus punishment and compliance behavior: the mediating role of affective attitude and the moderating role of operational capabilities of artificial intelligence
Authors: Zhu Nan , Liu Yuxin , Zhang Jianwei , Wang Na
Published: September 2023

Previous research has long focused on the positive effect of contingent reward on employees’ psychological states and outcomes. Recent studies show that contingent punishment can also positively impact employees’ outcomes. Whether contingent reward can improve employees’ compliance behavior more than punishment can, has not been adequately studied. Exploring this issue can help researchers understand contingent reward and punishment from the perspective of the relationship norms between leaders and employees. Drawing on the planned behavior theory and cognitive appraisal theory, we developed and tested a model specifying why and how contingent reward (relative to contingent punishment) increase employees’ compliance behavior. Using a scenario-based experiment across two-stage surveys of 309 participants, we found that contingent reward (relative to contingent punishment) could influence compliance behavior by increasing and decreasing distinct types of affective attitudes (i.e., self-esteem and anxiety). Moreover, the perceived operational capabilities of artificial intelligence (AI) moderated the effect of contingent reward on self-esteem and anxiety. High perceived operational capabilities of AI enhanced the positive effect of contingent reward (relative to contingent punishment) on self-esteem and its negative effect on anxiety as well. This research yields innovative insights for the improvement of compliance behavior.
Permeameter and solenoid measurements of Epstein strips of electrical steels
Authors: Chen Du-Xing , Zhu Yong-Hong
Published: September 2023

The dc and ac flux density vs magnetic field B(H) loops of Epstein electrical strips are measured in an IEC type-A permeameter with a high-quality electrical strip wound double yokes of inside length l0 = 0.2 m and inside height h0 = 0.1 m and in a long solenoid. The relevant demagnetizing and eddy-current effects are analyzed, modeled, and discussed. It is concluded that demagnetizing corrected solenoid measurement developed for determining dc B(H) loops of the material cannot be used for the ac case, owing to complicated eddy-current demagnetizing effects. Permeameter-measured ac B(H) loops with H detected by a flat H-coil of length less than l0/2 touching the strip’s middle surface may be considered representative of the actual material because H is very uniform along the strip within 3l0/4. Strips with ac B(H) loops thus determined should be used to calibrate the effective magnetic path length lm of Epstein measurements, where a very nonuniform field is applied to the strips.
Magnetic force-based cell manipulation for in vitro tissue engineering
Authors: Hu Huiqian , Krishaa L. , Fong Eliza Li Shan
Published: September 2023

Cell manipulation techniques such as those based on three-dimensional (3D) bioprinting and microfluidic systems have recently been developed to reconstruct complex 3D tissue structures in vitro. Compared to these technologies, magnetic force-based cell manipulation is a simpler, scaffold- and label-free method that minimally affects cell viability and can rapidly manipulate cells into 3D tissue constructs. As such, there is increasing interest in leveraging this technology for cell assembly in tissue engineering. Cell manipulation using magnetic forces primarily involves two key approaches. The first method, positive magnetophoresis, uses magnetic nanoparticles (MNPs) which are either attached to the cell surface or integrated within the cell. These MNPs enable the deliberate positioning of cells into designated configurations when an external magnetic field is applied. The second method, known as negative magnetophoresis, manipulates diamagnetic entities, such as cells, in a paramagnetic environment using an external magnetic field. Unlike the first method, this technique does not require the use of MNPs for cell manipulation. Instead, it leverages the magnetic field and the motion of paramagnetic agents like paramagnetic salts (Gadobutrol, MnCl2, etc.) to propel cells toward the field minimum, resulting in the assembly of cells into the desired geometrical arrangement. In this Review, we will first describe the major approaches used to assemble cells in vitro—3D bioprinting and microfluidics-based platforms—and then discuss the use of magnetic forces for cell manipulation. Finally, we will highlight recent research in which these magnetic force-based approaches have been applied and outline challenges to mature this technology for in vitro tissue engineering.
Human gut epithelium features recapitulated in MINERVA 2.0 millifluidic organ-on-a-chip device
Authors: Donnaloja Francesca , Izzo Luca , Campanile Marzia , Perottoni Simone , Boeri Lucia , Fanizza Francesca , Sardelli Lorenzo , Jacchetti Emanuela , Raimondi Manuela T. , Rito Laura Di , Craparotta Ilaria , Bolis Marco , Giordano Carmen , Albani Diego
Published: September 2023

We developed an innovative millifluidic organ-on-a-chip device, named MINERVA 2.0, that is optically accessible and suitable to serial connection. In the present work, we evaluated MINERVA 2.0 as millifluidic gut epithelium-on-a-chip by using computational modeling and biological assessment. We also tested MINERVA 2.0 in a serially connected configuration prodromal to address the complexity of multiorgan interaction. Once cultured under perfusion in our device, human gut immortalized Caco-2 epithelial cells were able to survive at least up to 7 days and form a three-dimensional layer with detectable tight junctions (occludin and zonulin-1 positive). Functional layer development was supported by measurable trans-epithelial resistance and FITC-dextran permeability regulation, together with mucin-2 expression. The dynamic culturing led to a specific transcriptomic profile, assessed by RNASeq, with a total of 524 dysregulated transcripts (191 upregulated and 333 downregulated) between static and dynamic condition. Overall, the collected results suggest that our gut-on-a-chip millifluidic model displays key gut epithelium features and, thanks to its modular design, may be the basis to build a customizable multiorgan-on-a-chip platform.
Electro-optic non-reciprocal polarization rotation in lithium niobate
Authors: Örsel Oğulcan E. , Bahl Gaurav
Published: September 2023

Polarization is a fundamental degree of freedom for light and is widely leveraged in free space and fiber optics. Non-reciprocal polarization rotation, enabled via the magneto-optic Faraday effect, has been essentially unbeatable for broadband isolators and circulators. For integrated photonics foundries, however, there is still no good path to producing low-loss magneto-optic components, which has prompted a search for alternatives that do not use polarization rotation. Moreover, magneto-optic materials tend to be highly lossy, and while large (10–100 rad/cm) polarization rotation can be achieved, the key figure of merit (rotation-per-loss) is typically <1 rad/dB. Here, we demonstrate that broadband non-reciprocal polarization rotation can be produced using electro-optics in nanophotonic devices. Our demonstration leverages electro-optic inter-polarization scattering around 780 nm in lithium niobate, in which the reciprocity is broken with the help of a radiofrequency stimulus that carries synthetic momentum. While the demonstrated electro-optic polarization rotation rate is ≈1 rad/cm, the exceptionally low loss of lithium niobate enables non-reciprocal polarization rotators with figures of merit that are 1-2 orders of magnitude better than what is possible with magneto-optics. This approach can be replicated on III–V platforms, paving the way for high-performance lasers with co-integrated monolithic non-reciprocal devices.
Origin of electrical noise near charge neutrality in dual gated graphene device
Authors: Mehra Aaryan , Mathew Roshan Jesus , Kumar Chandan
Published: September 2023

This Letter investigates low frequency 1/f noise in an hBN encapsulated graphene device in a dual gated geometry. The noise study is performed as a function of top gate carrier density (nTG) at different back gate density (nBG). The noise at low nBG is found to be independent of top gate carrier density. With increasing nBG, noise value increases, and a noise peak is observed near charge inhomogeneity of the device. A further increase in nBG leads to a decrease in noise magnitude. The shape of the noise is found to be closely related to a charge inhomogeneity region of the device. Moreover, the noise and conductivity data near charge neutrality show clear evidence of noise emanating from a combination of charge number and mobility fluctuation.
On a magnetic Lieb–Thirring-type estimate and the stability of bipolarons in graphene
Authors: Alves Magno B. , Del Cima Oswaldo M. , Franco Daniel H. T. , Pereira Emmanuel
Published: September 2023

Two-dimensional Weyl–Dirac relativistic fermions have attracted tremendous interest in condensed matter as they mimic relativistic high-energy physics. This paper concerns two-dimensional Weyl–Dirac operators in the presence of magnetic fields, in addition to a short-range scalar electric potential of the Bessel–Macdonald-type, restricted to its positive spectral subspace. This operator emerges from the action of a pristine graphene-like QED3 model recently proposed by De Lima, Del Cima, and Miranda, “On the electron–polaron–electron–polaron scattering and Landau levels in pristine graphene-like quantum electrodynamics,” Eur. Phys. J. B93, 187 (2020). A magnetic Lieb–Thirring-type inequality à la Shen is derived for the sum of the negative eigenvalues of the magnetic Weyl–Dirac operators restricted to their positive spectral subspace. An application to the stability of bipolarons in graphene in the presence of magnetic fields is given.
Symmetric and asymmetric separated variables. II. A second integrable case of the complex Kirchhoff model
Authors: Skrypnyk T.
Published: September 2023

In the present paper, we find a second new integrable case of the complex Kirchhoff model on e*(3). We show that the obtained integrable model possesses two types of separation of variables (SoV): symmetric and asymmetric ones. The asymmetric SoV—similar to that of the Clebsch model (F. Magri and T. Skrypnyk, arXiv:1512.04872) and of the first integrable case of the complex Kirchhoff model (T. Skrypnyk, J. Geom. Phys. 172, 104418 (2022)]—is characterized by two different curves of separation. In the case of symmetric SoV, both curves of separation are the same. This case—similar to the integrable case of the complex Kirchhoff model of Skrypnyk, J. Geom. Phys. 172, 104418 (2022)—yields a direct analog of the famous Weber–Neumann separated coordinates. The obtained separation curves and Abel-type equations for the constructed model can be viewed as trigonometric degenerations of the corresponding separation curves and Abel-type equations of the Clebsch model [F. Magri and T. Skrypnyk, arXiv:1512.04872 and T. Skrypnyk, J. Geom. Phys. 135, 204–218 (2019)], while separation curves and Abel-type equations of Skrypnyk, J. Geom. Phys. 172, 104418 (2022) can be viewed as their rational degenerations.
Correlations between asymmetric compression, burn amplification, and hot-spot velocities in inertial confinement fusion implosions
Authors: Nora R. C. , Birge N. , Casey D. , Danly C. , Dewald E. L. , Djordjevic B. Z. , Do A. , Durocher M. , Field J. E. , Fittinghoff D. , Freeman M. S. , Gaffney J. , Geppert Kleinrath V. , Haan S. , Hahn K. , Hartouni E. , Hohenberger M. , Kerr S. , Landen O. L. , Milovich J. , Moore A. S. , Patel P. , Schlossberg D. J. , Sepke S. M. , Spears B. K. , Volegov P. L. , Wilde C.
Published: September 2023

This manuscript examines the correlations between the hot-spot velocity (an observable signature of residual kinetic energy), low-mode implosion asymmetries, and burn amplification in inertial confinement fusion implosions on the National Ignition Facility (NIF). Using a combination of two-dimensional axis-symmetric and three-dimensional radiation-hydrodynamic simulations coupled to neutronics, we find that for typical NIF implosions, the stagnation asymmetry multiplies the observed hot-spot velocity anywhere from 80% to 120%, while burn amplification always increases it. Additionally, we find stagnation asymmetry typically deflects the observed hot-spot flow. The two mechanisms (low-mode implosion asymmetries and burn amplification) can be decoupled, and application of a simple model to a database of cryogenic implosions on the NIF infers the total hot-spot velocity amplification. This finding modifies the interpretation of data collected from inertial confinement fusion experiments and impacts the magnitude and origin of low-mode asymmetries.
Detection of vortex charge and beam displacement by wavefront division interferometry
Authors: Chatterjee Kalipada , Singh Rakesh Kumar , Jha Rajan
Published: September 2023

In this work, a wavefront division interferometry method for determining the topological charge (l) of vortex beams (VB) is proposed and utilized for the detection of beam displacement. The method uses Fresnel biprism as a single element to determine vortex charge for up to l = ±10. Additionally, the interference pattern configuration is utilized to detect beam displacement in orthogonal directions. To accurately determine the shift in pattern due to beam displacement, a fringe scanning algorithm based on image correlation is proposed. The algorithm quantifies the fringe shift in terms of pixel units that is used to estimate the beam displacement. Sensitivity of 80 px/0.5 mm beam displacement along the x-direction is achieved with the system. The proposed method is single ended that can be integrated with optical assemblies for fast VB recognition. Furthermore, the displacement sensing utility could be used for precision alignment, propagation analysis, and monitoring physical fields.
Design of a high counting efficiency sensor for 1.0 cubic feet per minute laser particle counter
Authors: Zheng Yanchang , Wu Guo , Chen Yesheng , Lu Yuelin , Li Cheng , Wan Guibo , Yin Rongxin
Published: September 2023

Based on the theory of Mie scattering, an optical sensor for a 1.0 cubic feet per minute laser particle counter is developed in this paper. First, an illumination optical path relying on aspherical lens and cylindrical lens for laser shaping was designed, and a narrow optical spot with the illumination in the vertical direction of the photosensitive area approximately distributed as a flat top was obtained. Second, the scattering light path was designed by using the theory of Mie scattering and geometric optics method. Then, the structure of the sampling air path was designed with reference to the principle of Laval nozzle, and the particle flow trajectory was verified by simulation using the fluid dynamics software Ansys Fluent. Finally, the performance of the optical sensor was measured with polystyrene latex (PSL) particles, and the results showed that the counting efficiency of the 0.3 μm particle size channel met the requirement of 50% ± 20% and the 0.5 μm particle size channel met the requirement of 100% ± 10%, which complied with the ISO 21501-4 standard.
Localization for random quasi-one-dimensional models
Authors: Boumaza H.
Published: September 2023

In this Review Article, we review the results of Anderson localization for different random families of operators that enter the framework of random quasi-one-dimensional models. We first recall what is Anderson localization from both physical and mathematical points of view. From the Anderson–Bernoulli conjecture in dimension 2, we justify the introduction of quasi-one-dimensional models. Then, we present different types of these models: the Schrödinger type in the discrete and continuous cases, the unitary type, the Dirac type, and the point interaction type. We present tools coming from the study of dynamical systems in dimension one: the transfer matrix formalism, the Lyapunov exponents, and the Furstenberg group. We then prove a criterion of localization for quasi-one-dimensional models of Schrödinger type involving only geometric and algebraic properties of the Furstenberg group. Then, we review results of localization, first for Schrödinger-type models and then for unitary type models. Each time, we reduce the question of localization to the study of the Furstenberg group and show how to use more and more refined algebraic criteria to prove the needed properties of this group. All the presented results for quasi-one-dimensional models of Schrödinger type include the case of Bernoulli randomness.
Evolution of coupled weakly driven waves in a dissipative plasma
Authors: Pham N. M. , Duarte V. N.
Published: September 2023

The nonlinear collisional dynamics of coupled driven plasma waves in the presence of background dissipation is studied analytically within kinetic theory. Sufficiently near marginal stability, phase space correlations are poorly preserved and time delays become unimportant. The system is then shown to be governed by two first-order coupled autonomous differential equations of cubic order for the wave amplitudes and two complementary first-order equations for the evolution of their phases. That system of equations can be decoupled and further simplified to a single second-order differential equation of Liénard's type for each amplitude. Numerical solutions for this equation are obtained in the general case, while analytic solutions are obtained for special cases in terms of parameters related to the spacing of the resonances of the two waves in frequency space, e.g., wave lengths and oscillation frequencies. These parameters are further analyzed to find classes of quasi-steady saturation and pulsating scenarios. To classify equilibrium points, local stability analysis is applied, and bifurcation conditions are determined. When the two waves saturate at similar amplitude levels, their combined signal is shown to invariably exhibit amplitude beating and phase jumps of nearly π. The obtained analytical results can be used to benchmark simulations and to interpret eigenmode amplitude measurements in fusion experiments.
Simulations of laser-driven strong-field QED with Ptarmigan: Resolving wavelength-scale interference andγ-ray polarization
Authors: Blackburn T. G. , King B. , Tang S.
Published: September 2023

Accurate modeling is necessary to support precision experiments investigating strong-field QED phenomena. This modeling is particularly challenging in the transition between the perturbative and nonperturbative regimes, where the normalized laser amplitude a0 is comparable to unity and wavelength-scale interference is significant. Here, we describe how to simulate nonlinear Compton scattering, Breit–Wheeler pair creation, and trident pair creation in this regime, using the Monte Carlo particle-tracking code Ptarmigan. This code simulates collisions between high-intensity lasers and beams of electrons or γ rays, primarily in the framework of the locally monochromatic approximation. We benchmark our simulation results against full QED calculations for pulsed plane waves and show that they are accurate at the level of a few per cent, across the full range of particle energies and laser intensities. This work extends our previous results to linearly polarized lasers and arbitrary polarized γ rays.
Prestrain-induced bistability in the design of tensegrity units for mechanical metamaterials
Authors: Micheletti Andrea , dos Santos Filipe A. , Guest Simon D.
Published: September 2023

Tensegrity metamaterials are a type of artificial materials that can exploit the tunable nonlinear mechanical behavior of the constituent tensegrity units. Here, we present reduced-order analytical models describing the prestrain-induced bistable effect of two particular tensegrity units. Closed-form expressions of the critical prestrain at which a unit transitions into a bistable regime are derived. Such expressions depend only on the geometry of the units. The predictions of the reduced-order model are verified by numerical simulations and by the realization of physical models. The present results can be generalized to analogous units with polygonal base, and the proposed tensegrity units can be assembled together to form one-dimensional metamaterials with tailorable nonlinear features such as multistability and solitary wave propagation.
Coexistence of stationary Görtler and crossflow instabilities in boundary layers
Authors: Uy Ken Chun Kit , Hao Jiaao , Wen Chih-Yung
Published: September 2023

The coexistence of stationary Görtler and crossflow instabilities in boundary layers covering incompressible to hypersonic regimes is investigated by varying the local sweep angle, pressure gradient, wall curvature, and wall temperature using linear stability analysis. The results show that increasing the local sweep angle under a fixed concave curvature in incompressible boundary layers leads to the appearance of two unstable modes at certain sweep angles, which is conventionally known as the “changeover” regime between the crossflow and Görtler modes. This study identifies a synchronization between the two modes under this condition, which is similar to multiple Görtler modes and thus referred to as Görtler–crossflow modes. Three scenarios are presented to describe the possible development of these modal instabilities. In addition, increasing the concave curvature destabilizes the instability, while introducing a pressure gradient stabilizes the instability and results in a shrinkage of the unstable band of the spanwise wavenumber, as reported in the literature. In supersonic and hypersonic boundary layers, synchronization can occur near specific sweep angles and under cold wall conditions in supersonic boundary layers. As Mach number increases, the synchronization regime shifts toward lower sweep angles and wall temperature, in which the former reflects a decline in crossflow strength relative to Görtler instability, while the latter indicates the influence of thermal effects on synchronization. In hypersonic boundary layers, the crossflow instability is insignificant compared with the Görtler instability. No synchronization is identified under various parameter changes, and the first Görtler–crossflow mode dominates across the entire spanwise wavenumber ranges.
Scaling analysis for azimuthal spreading and contact time of droplet impacting on superhydrophobic cylindrical surfaces
Authors: Naveen P. T. , Harikrishnan A. R.
Published: September 2023

Drop impact on superhydrophobic surfaces has gained great attention because of its physics and application in water repellency, drag reduction, and anti-icing. Spreading lengths and the contact time are the crucial parameters determining the extend of drop–surface interaction and effective heat transfer between the two and are, hence, trivial to many engineering applications. Post-collisional dynamics over cylindrical geometries are quite different from that of the flat surfaces due to the asymmetry in spreading and retraction dynamics. The dynamics are mainly governed by the impact Weber number and curvature ratio of impacting surface to drop. The spreading dynamics in axial direction is found to be fairly predicted by the governing laws coined for flat surfaces. However, the spreading dynamics in the azimuthal direction is quite complex. Herein, we propose a simple scaling analysis for the spreading dynamics in the azimuthal direction as well as for the contact time of the impacting drop with the surface. A modified capillary length is proposed accounting the curvature effect of the substrate by incorporating a centrifugal component of acceleration for the expanding lamella over the curved surface. With the proposed modified capillary length, a universal scaling relationship for azimuthal spreading length and contact time is developed. The proposed scaling laws are found to be in good agreement with the experimental results from the present study as well as with the existing literature for a wide range of Weber numbers and surface curvature.
Resonant optical reflection from a GaN/(Al,Ga)N excitonic Bragg structure
Authors: Ivanov A. A. , Chaldyshev V. V. , Zavarin E. E. , Sakharov A. V. , Lundin W. V. , Tsatsulnikov A. F.
Published: September 2023

We experimentally demonstrate the formation of a superradiant optical mode in the room-temperature reflection spectra from a resonant Bragg structure composed of 30 equidistant GaN quantum wells separated by (Al,Ga)N barriers. The mode arises when the condition of the Bragg diffraction is fulfilled at the wavelength corresponding to the energy of the quasi-two-dimensional excitons in the quantum wells. It manifests itself as a significant increase in the amplitude and a change in the shape of the resonant optical reflection due to the electromagnetic coupling of the excitons. By modeling of the optical spectra, we evaluate the radiative and non-radiative broadening parameters of the excitonic states in the GaN quantum wells, which appear to be 0.4 ± 0.02 and 40 ± 5 meV, correspondingly, for the resonant exciton energy of 3.605 eV. The resonant Bragg structure based on the periodic sequence of the GaN quantum wells demonstrates an efficient coupling of photons and excitons at room temperature, which makes it promising for device applications.
Slicing of a soft solid
Authors: Li Meng , Karnal Preetika , Lu Yinan , Hui Chung-Yuen , Jagota Anand
Published: September 2023

Cutting of soft materials is a complex problem, which is still not well understood at the fundamental level, especially for soft materials. The cutting process we consider is slicing, which starts with indentation, followed by sliding of a knife on the material to be cut. Here, we describe cutting experiments on PDMS elastomers with three different moduli. Our experiments reveal typical stages of this cutting process, starting with indentation and ending at steady state cutting. The process starts with a pre-cutting phase in which the blade does not slip grossly relative to the solid to be cut, and deformation is mostly elastic. Slip of the blade initiates suddenly and is often accompanied by initiation of cutting. Cutting is relatively smooth in the next stage, which requires a continuous increase in shear force. For soft PDMS, this smooth cutting stage is followed by one in which folds or creases form on the cutting surface. The corresponding shear force response is no longer smooth as “steady” sliding occurs in a stick–slip fashion with oscillatory forces. The average shear force reaches a plateau and no longer increases with shear displacement. Experimental observations of the various cutting stages are interpreted quantitatively.
Numerical simulation of coupling behavior in coaxial hybrid arc welding apparatus
Authors: Wu XingPei , Liu ZuMing , Jia ChuanBao
Published: September 2023

Double-layer coaxial hybrid arcing technology has been developed based on an inner constraint arc and an outer ring arc; the heat and pressure properties of the arc source are supposed to be decoupled and leading to improved controllability of the weld pool thermal-force state. But, the coupling state between the two arcs is not uncovered, and the process window for stable hybrid arc is narrow. In this study, a numerical model of the coaxial hybrid arc system is established, the influence of the water-cooled nozzle on the arc is considered, and the model's accuracy is verified by the measured arc pressure. The physical fields, such as temperature, velocity, and current density distribution, of the hybrid arc are calculated, and the influence of the inner constraint arc current or outer ring arc current on arc pressure and the coupling state in the hybrid arc are uncovered. It was found that (1) at the center of the stable hybrid arc, the current density, magnetic flux intensity, Lorentz force, and arc pressure with a rise in constraint arc current are higher than with a rise in outer arc current; (2) given the total current, adjust the proportion of the inner or outer arc currents, the total heat input basically remains unchanged; and (3) the cause of the arc collapse phenomenon, which is challenging to explain experimentally: the non-ionized gas layer in the orifice throat is broken through.
Flow and heat transfer in Phan-Thien–Tanner viscoelastic fluid around a rotating hot cylinder in a square enclosure
Authors: Arshadi Amir , Nili-Ahmadabadi Mahdi , Minaeian Ali , Norouzi Mahmood , Ha Man Yeong
Published: September 2023

Flow and heat transfer problems in non-Newtonian fluids are considerably more complicated compared to Newtonian fluids due to their non-linear behavior and complex properties. This paper numerically studied the flow and heat transfer of a viscoelastic fluid around a hot rotating cylinder in a square enclosure. The Phan-Thien–Tanner (PTT) model, one of the most accurate models available to describe the behavior of viscoelastic fluids, was used to obtain the constitutive equations of the viscoelastic fluid, which were then solved by using the finite-volume method with the Rheoheatfoam solver of the OpenFOAM software. The log-conformation approach was employed to avoid the divergence problem at high Weissenberg numbers. Simulations were conducted to investigate the effects of the Weissenberg number, Brinkman number, Reynolds number, and the ratio of the polymeric viscosity to total viscosity on the behavior of fluid flow and heat transfer. The results showed that increasing the Weissenberg number led to a higher shear thinning effect, which decreased the fluid's effective viscosity and viscous dissipation near the cylinder. As a result, heat transfer from the cylinder increased, and the frictional torque applied to the cylinder decreased. However, the shear thinning effect was negligible when the Weissenberg number exceeded 100. Furthermore, the tangential normal stress significantly increased as the Weissenberg number increased up to one. However, with further increases in the Weissenberg number, the tangential normal stress reduced, eventually reaching close to zero at high Weissenberg numbers.
An agile radio-frequency source using internal linear sweeps of a direct digital synthesizer
Authors: Huegler Ethan , Hill Joshua C. , Meyer David H.
Published: September 2023

Agile rf sources are a common requirement for control systems in quantum science and technology platforms. The direct digital synthesizer (DDS) often fills this role by allowing programmable control of the rf signals. Due to limitations of the DDS architecture, implementing an agile rf source requires rapid and precisely-timed programming of discrete updates that restrict the source’s agility. Here, we describe a microcontroller-based interface that exploits the DDS’s internal linear sweep accumulator to perform both sequential linear sweeps and standard discrete updates at the ∼10μs scale. This allows updates to the swept parameter as fast as every 8 ns with greatly reduced communication and memory overhead. We demonstrate the utility of this system by using it as the reference of an optical phase-locked loop to implement rapid, adjustable laser frequency sweeps in a Rydberg electromagnetically induced transparency spectroscopy measurement.
Chiral molecule candidates for trapped ion spectroscopy byab initiocalculations: From state preparation to parity violation
Authors: Landau Arie , Eduardus  , Behar Doron , Wallach Eliana Ruth , Pašteka Lukáš F. , Faraji Shirin , Borschevsky Anastasia , Shagam Yuval
Published: September 2023

Parity non-conservation (PNC) due to the weak interaction is predicted to give rise to enantiomer dependent vibrational constants in chiral molecules, but the phenomenon has so far eluded experimental observation. The enhanced sensitivity of molecules to physics beyond the Standard Model (BSM) has led to substantial advances in molecular precision spectroscopy, and these may be applied to PNC searches as well. Specifically, trapped molecular ion experiments leverage the universality of trapping charged particles to optimize the molecular ion species studied toward BSM searches, but in searches for PNC, only a few chiral molecular ion candidates have been proposed so far. Importantly, viable candidates need to be internally cold, and their internal state populations should be detectable with high quantum efficiency. To this end, we focus on molecular ions that can be created by near threshold resonant two-photon ionization and detected via state-selective photo-dissociation. Such candidates need to be stable in both charged and neutral chiral versions to be amenable to these methods. Here, we present a collection of suitable chiral molecular ion candidates we have found, including CHDBrI+ and CHCaBrI+, that fulfill these conditions according to our ab initio calculations. We find that organo-metallic species have low ionization energy as neutrals and relatively high dissociation thresholds. Finally, we compute the magnitude of the PNC values for vibrational transitions for some of these candidates. An experimental demonstration of state preparation and readout for these candidates will be an important milestone toward measuring PNC in chiral molecules for the first time.
Single-file transport of binary hard-sphere mixtures through periodic potentials
Authors: Voráč David , Maass Philipp , Ryabov Artem
Published: September 2023

Single-file transport occurs in various scientific fields, including diffusion through nanopores, nanofluidic devices, and cellular processes. We here investigate the impact of polydispersity on particle currents for single-file Brownian motion of hard spheres when they are driven through periodic potentials by a constant drag force. Through theoretical analysis and extensive Brownian dynamics simulations, we unveil the behavior of particle currents for random binary mixtures. The particle currents show a recurring pattern in dependence of the hard-sphere diameters and mixing ratio. We explain this recurrent behavior by showing that a basic unit cell exists in the space of the two hard-sphere diameters. Once the behavior of an observable inside the unit cell is determined, it can be inferred for any diameter. The overall variation of particle currents with the mixing ratio and hard-sphere diameters is reflected by their variation in the limit where the system is fully covered by hard spheres. In this limit, the currents can be predicted analytically. Our analysis explains the occurrence of pronounced maxima and minima of the currents by changes in the effective potential barrier for the center-of-mass motion.
Evolution of turbulent liquid films on the corrugated plate—rivulets and slender water columns necking rupture
Authors: Zeng Jie , Wang Yi-fei , Li Ting-ting , Wei Zong-yao , Yu Guang-suo , Wang Fu-chen , Wang Zhi-min , Hou Mao-lin , Yuan Hong-nian
Published: September 2023

The evolution of turbulent liquid film on the corrugated plate is experimentally studied with the help of ultrasonic Doppler velocimetry and a high-speed camera, revealing the formation mechanism of rivulets and water columns necking rupture. The results show that the flow pattern of the liquid film on the corrugated plate is divided into three regions: stable region, fluctuating region, and oscillating region. In the fluctuating region, the connection between adjacent solitary waves leads to the generation of primary rivulets. In contrast, the formation of secondary rivulets mainly comes from the extinction of solitary waves. In the oscillating region, the collision between secondary rivulets promotes the formation of slender water columns. The necking diameter of the water column tended to decrease exponentially with time. The increase in Rel (liquid phase Reynolds number) promotes the necking rupture process of the water column due to the presence of corrugated structures. When Rel increased from 1.72 × 104 to 2.57 × 104, the characteristic time of necking rupture was shortened by about 25.7%.
Multi-particle collision dynamics for a coarse-grained model of soft colloids applied to ring polymers
Authors: Sappl Lisa , Likos Christos N. , Zöttl Andreas
Published: September 2023

The simulation of polymer solutions often requires the development of methods that accurately include hydrodynamic interactions. Resolution on the atomistic scale is too computationally expensive to cover mesoscopic time and length scales on which the interesting polymer phenomena are observed. Therefore, coarse-graining methods have to be applied. In this work, the solvent is simulated using the well-established multi-particle collision dynamics scheme, and for the polymer, different coarse-graining methods are employed and compared against the monomer resolved Kremer–Grest model by their resulting diffusion coefficients. This research builds on previous work [Ruiz-Franco et al., J. Chem. Phys. 151, 074902 (2019)], in which star polymers and linear chains in a solvent were simulated and two different coarse-graining methods were developed, in order to increase computational efficiency. The present work extends this approach to ring polymers and seeks to refine one of the authors’ proposed model: the penetrable soft colloid model. It was found that both proposed models are not well suited to ring polymers; however, the introduction of a factor to the PSC model delivers satisfying results for the diffusion behavior by regulating the interaction intensity with the solvent.
Growth of ultrathin Mn4N epitaxial films on SrTiO3(001) and their thickness-dependent magnetic structures
Authors: Yasuda Tomohiro , Amemiya Kenta , Suemasu Takashi
Published: September 2023

Mn4N thin films meet the requirements for efficient current-driven magnetic domain wall motion, such as perpendicular magnetic anisotropy and small magnetization. To demonstrate efficient field-free spin–orbit torque (SOT)-driven domain wall motion, the thickness of the Mn4N layer must be reduced. In this study, we focus on the fabrication of Mn4N ultrathin films on SrTiO3(001) substrates and demonstrate the epitaxial growth of Mn4N films as thin as around 4 nm. Surprisingly, the sign of the anomalous Hall resistivity of Mn4N reverses when the thickness of Mn4N decreases from approximately 8 to 4 nm. X-ray magnetic circular dichroism measurements suggest that the magnetic structure of Mn4N with a thickness of around 4 nm is different from that of conventional ferrimagnetic Mn4N films. The results obtained in this study are of great importance when considering the use of SOT and the interfacial Dzyaloshinskii–Moriya interaction in Mn4N ultrathin films.
Optimum spacing for maximum heat transfer density in tube bundle
Authors: Alam Md. Mahbub
Published: September 2023

The optimal spacing between tubes in a tube bundle is of fundamental and practical importance. This paper numerically investigates heat transfer, fluid dynamics, fluid forces, vortex shedding frequency, optimum spacing, and relationship between flow structures and heat transfer from a group of tubes in a tube bundle for the radial gap spacing ratio g* (=g/d) = 0.1–5, where d is the diameter of a tube. The key objective is to find the optimum g* for maximum heat transfer density. The heat transfer from the tubes is highly sensitive to g*. With increasing g*, the heat transfer density first increases and reaches a peak before declining, yielding the optimum spacing at g* = 0.5 (void fraction, VF = 0.56) or g* = 0.6 (VF = 0.60) depending on the tube orientations with respect to the flow. The small tubes with g* > 0.25 perform better in view of heat transfer than the big tube of the bundle diameter. In addition, g* effects on fluid forces, vortex shedding frequencies, and wake structure and their relationships with heat transfer are discussed in detail.
Dynamics of molecular collisions in air and its mean free path
Authors: Tsalikis Dimitrios G. , Mavrantzas Vlasis G. , Pratsinis Sotiris E.
Published: September 2023

The mechanics and dynamics of molecular collisions in air are investigated by thoroughly validated atomistic molecular dynamics (MD) simulations that treat oxygen and nitrogen as true diatomic molecules accounting for their non-spherical shape and, most importantly, force field. Due to their rotational motion and non-spherical shape, molecules follow complex trajectories at close enough separations experiencing a great variety of collision events. Most of the collisions are bimolecular. However, some can involve up to four molecules as pairs (or even triplets) of molecules that collide repeatedly are observed. Following their initial encounter, these molecules separate briefly, come back, and collide again and again creating even “orbiting” collisions, before they split apart to collide with other molecules. Identifying such rather spurious collisions and filtering them by hazard plot analysis was a key step in correctly determining collision densities and accumulating collision event statistics. By systematically recording the distribution of free paths (distances traveled by molecules between genuine collisions), the mean free path, λ, of air is determined as 38.5 ± 1 nm at 300 K and 1 atm. This is 43% smaller than the 67.3 nm widely accepted λ today at these conditions and quite robust to the employed MD force field as long as it accurately matches the experimentally determined macroscopic properties of air (density, viscosity, and diffusivity).
Experimental study on radial diffusion characteristics of diesel–pentanol spray
Authors: Li Fengyu , Tian Junjian , Lin Qizhao
Published: September 2023

It is always a hot topic to find alternative fuel for diesel. Pentanol is a potential alternative fuel for diesel. In this study, different volume ratios of fuel were obtained by adding pentanol to diesel. On the high-pressure common rail experimental platform, the spray processes of pure diesel and diesel–pentanol blends were observed and analyzed, and the differences of radial diffusion capability between different experimental fuel sprays were evaluated. The maximum radial diffusibility was analyzed through the maximum width and the maximum width corresponding to the axial position. The radial diffusion capacity of the whole was analyzed by means of the average width and spray cone angle, and the area of the gas entrainment area was analyzed. The results showed that the addition of pentanol enhanced the radial diffusion ability and gas entrainment ability of diesel sprays.
Aeroacoustic investigation of airfoil at near-stall conditions
Authors: Jaiswal Prateek , Rendón Jose , Moreau Stéphane
Published: September 2023

This paper presents a detailed aeroacoustic investigation of a controlled-diffusion airfoil at near-stall condition. The study aims at answering two research questions: identify the flow mechanism responsible for separation noise for an airfoil near-stall conditions and whether the noise is generated by a dipole for airfoil close to stall and can be quantified by Amiet's diffraction theory. The study uses synchronized particle image velocimetry, remote microphone probes, and far-field microphone measurements to perform experiments at two chord-based Reynolds numbers of about 150 000 and 250 000. The results show that when the airfoil is placed at a higher angle of attack, such as 15°, strong amplification of flow disturbance is seen, resulting in the rolling up of the shear layer in the aft region of the airfoil, forming large coherent structures. While these rollers play a central role in the increase in noise due to flow separation, the flapping of shear layer does not contribute to the separation noise. The present study conclusively shows that separation noise is dipolar in nature and that the quadrupolar contribution for low-speed airfoils at near-stall conditions can be neglected. However, the increase in flow disturbances measured close to the trailing edge of the airfoil implies that the assumption of small-amplitude disturbance is no longer valid, which is the central premise of the thin linearized airfoil theory. Outside the frequency range at which flow separation operates, Amiet's theory is able to predict the far-field noise even at high angles of attack.
Role of surface tension effect at the deformed free surface of chemotaxis coupling flow system: Weakly nonlinear study
Authors: Chakraborty Symphony , Ivančić Filip , Chou Yi-Ju
Published: September 2023

A comprehensive study is presented on pattern formation during the initial stages of bioconvection in chemotaxis suspensions influenced by surface tension based on the linear stability analysis done by Chakraborty and Sheu [J. Fluid Mech. 923, A14 (2021)]. We explore the intricate patterns arising when suspended oxytactic bacteria (e.g., Bacillus subtilis) are introduced into an open chamber, unveiling a compelling bioconvection phenomenon. This process stems from the bacteria's response to higher oxygen concentrations near the free surface, driving density fluctuations akin to the Rayleigh–Taylor instability. Our investigation employs a weakly nonlinear stability analysis to reveal intricate dynamics arising from multi-parameter interactions, yielding captivating transformations. A bifurcation study reveals that unstable rolls undergo sub-critical bifurcation, giving rise to hexagonal patterns and a variety of hybrid formations. Notably, altering the chamber's length accentuates this diversity, yielding pattern formation, including both rolls and hexagons, driven by surface tension. Our findings underscore the pivotal role of surface tension in shaping pattern stability. Hexagonal patterns, inherently unstable, acquire stability under heightened surface tension (decreasing Caτ). Conversely, increased Frτ values disrupt their stability. Fascinatingly, surface tension prompts the emergence of distinct hexagon subcategories—up-hexagons and down-hexagons—each exhibiting unique responses to changes in SτHτ. Numerical simulations substantiate our theoretical insight, offering tangible proof of the complex dynamics of pattern formation, as the present study elucidates the interplay between surface tension and parameter effects governing pattern stability in bioconvection onset, thereby advancing comprehension and setting the foundation for future explorations.