Scale Separation Research Articles

Shedding light on dark bubble cosmology

Dark bubble cosmology is an alternative paradigm to compactification, which can circumvent issues of moduli stabilization and scale separation. In this paper we investigate how electromagnetic fields can be incorporated in this framework. Worldvolume fields backreact on the ambient universe in which the bubble expands, which in turn affects the energy-momentum distribution and the effective gravity induced on the brane. We compute these effects, showing that the resulting four-dimensional cosmology consistently includes electromagnetic waves.

Evolution of cooperation in deme-structured populations on graphs.

Understanding how cooperation can evolve in populations despite its cost to individual cooperators is an important challenge. Models of spatially structured populations with one individual per node of a graph have shown that cooperation, modeled via the prisoner's dilemma, can be favored by natural selection. These results depend on microscopic update rules, which determine how birth, death, and migration on the graph are coupled. Recently, we developed coarse-grained models of spatially structured populations on graphs, where each node comprises a well-mixed deme, and where migration is independent from division and death, thus bypassing the need for update rules. Here, we study the evolution of cooperation in these models in the rare-migration regime, within the prisoner's dilemma. We find that cooperation is not favored by natural selection in these coarse-grained models on graphs where overall deme fitness does not directly impact migration from a deme. This is due to a separation of scales, whereby cooperation occurs at a local level within demes, while spatial structure matters between demes.

Efficient computational homogenisation of 2D beams of heterogeneous elasticity using the patch scheme

Modern ‘smart’ materials have complex heterogeneous microscale structure, often with unknown macroscale closure but one we need to realise for large scale engineering and science. The multiscale Equation-Free Patch Scheme empowers us to non-intrusively, efficiently, and accurately predict large scale, system level, solutions through computations on only small sparse patches of the given detailed microscale system. Here the microscale system is that of a 2D beam of heterogeneous elasticity, with either fixed–fixed, fixed–free, or periodic boundary conditions. We demonstrate that the described multiscale Patch Scheme simply, efficiently, and stably predicts the beam’s macroscale, with a controllable accuracy, at finite scale separation. Dynamical systems theory supports the scheme. This article points the way for others to use this innovative systematic non-intrusive approach, via a developing toolbox of functions, to model and compute accurately macroscale system-levels of general complex physical and engineering systems.

Mitigation of Shock-Induced Separation Using Square-Shaped Micro-Serrations—A Preliminary Study

Suppressing shock-induced flow separation has been a long-standing problem in the design of supersonic vehicles. To reduce the structural and design complexity of control devices, a passive control technique based on micro-serrations is proposed and its controlling effects are preliminarily investigated under test conditions in which the Mach number is 2.5 and the ramp creating an incident shock is 15 deg. Meanwhile, a vorticity-based criterion for assessing separation scales is developed to resolve the inapplicability of the zero skin friction criterion caused by wall unevenness. The simulations demonstrate that the height of the first stair significantly influences the separation length. Generally, the separation length is shorter at higher stairs, but when the height is greater than half of the thickness of the incoming boundary layer, the corresponding separation point moves upstream. A stair with a height of only 0.4 times the thickness of the boundary layer reduces the separation length by 2.69%. Further parametric analysis reveals that while the remaining serrations have limited effects on the flow separation, an optimization of their shape (depth and width) can create more favorable spanwise vortices and offer a modest improvement of the overall controlling performance. Compared to the plate case, a 9.13% reduction in the separation length can be achieved using a slightly serrated design in which the leading stair is 0.1 high and the subsequent serrations are 0.2 deep and 0.05 wide (nondimensionalized, with the thickness of the incoming boundary layer). Meanwhile, the micro-serration structure even brings less drag. Considering the minor modification to the structure, the proposed method has the potential for use in conjunction with other techniques to exert enhanced control on separations.

Inflammatory Knee Synovitis: Evaluation of an Accelerated FLAIR Sequence Compared With Standard Contrast-Enhanced Imaging.

The aim of this study was to assess the diagnostic value and accuracy of a deep learning (DL)-accelerated fluid attenuated inversion recovery (FLAIR) sequence with fat saturation (FS) in patients with inflammatory synovitis of the knee. Patients with suspected knee synovitis were retrospectively included between January and September 2023. All patients underwent a 3 T knee magnetic resonance imaging including a DL-accelerated noncontrast FLAIR FS sequence (acquisition time: 1 minute 38 seconds) and a contrast-enhanced (CE) T1-weighted FS sequence (acquisition time: 4 minutes 50 seconds), which served as reference standard. All knees were scored by 2 radiologists using the semiquantitative modified knee synovitis score, effusion synovitis score, and Hoffa inflammation score. Diagnostic confidence, image quality, and image artifacts were rated on separate Likert scales. Wilcoxon signed rank test was used to compare the semiquantitative scores. Interreader and intrareader reproducibility were calculated using Cohen κ. Fifty-five patients (mean age, 52 ± 17 years; 28 females) were included in the study. Twenty-seven patients (49%) had mild to moderate synovitis (synovitis score 6-13), and 17 patients (31%) had severe synovitis (synovitis score >14). No signs of synovitis were detected in 11 patients (20%) (synovitis score <5). Semiquantitative assessment of the whole knee synovitis score showed no significant difference between the DL-accelerated FLAIR sequence and the CE T1-weighted sequence (mean FLAIR score: 10.69 ± 8.83, T1 turbo spin-echo FS: 10.74 ± 10.32; P = 0.521). Both interreader and intrareader reproducibility were excellent (range Cohen κ [0.82-0.96]). Assessment of inflammatory knee synovitis using a DL-accelerated noncontrast FLAIR FS sequence was feasible and equivalent to CE T1-weighted FS imaging.

Multiscale simulation scheme by using a finite-difference derivative framework for lubrication surface

To exactly describe lubrication problems modelling micro-scale influence in rough lubricated contact is unavoidable. In this study a novel computational scheme for lubricated problem is presented based on two-scale homogenization method, which facilitates solving the two-scale problem. Homogenization model of mass fluxes is implemented at the micro-scale domain, and represents the influence of surface topography. A linearization method is developed to derive finite derivatives of mass fluxes at the micro-scale domain defined by scale separation. The key strength of the proposed procedure is the finite difference derivative coupling which represents the lubricated problem inclusive of the effect of surface topography. The effectiveness of the proposed multiscale scheme is validated by comparing with the deterministic method. The numerical results show that increasing topography amplitude can improve the performance of journal bearing in terms of load carrying capacity and friction coefficient.

Local electroneutrality breakdown for electrolytes within varying-section nanopores

We determine the local charge dynamics of a z-z\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$z-z$$\\end{document} electrolyte embedded in a varying-section channel. By means of an expansion based on the length scale separation between the axial and transverse direction of the channel, we derive closed formulas for the local excess charge for both, dielectric and conducting walls, in 2D (planar geometry) as well as in 3D (cylindrical geometry). Our results show that, even at equilibrium, the local charge electroneutrality is broken whenever the section of the channel is not homogeneous for both dielectric and conducting walls as well as for 2D and 3D channels. Interestingly, even within our expansion, the local excess charge in the fluid can be comparable to the net charge on the walls. We critically discuss the onset of such local electroneutrality breakdown in particular with respect to the correction that it induces on the effective free energy profile experienced by tracer ions.Graphical abstract

Kinetic Energy Cascade Induced by the Interaction of Mean Flow, Topography, and Mesoscale Eddies East of Taiwan: A Scale-to-Scale Analysis

Abstract The scale-to-scale kinetic energy (KE) cascade induced by the nonlinear interaction among topography, the Kuroshio, and mesoscale eddies is systematically investigated in the coarse-graining framework based on simulated data from the well-validated Regional Ocean Model System. The KE transfer exhibits inhomogeneous spatial and temporal distributions and varies with length scale. During current–topography interaction, the KE transfers downscale across larger scales and reversely across smaller scales with an inherent separation scale of 150 km northeast of Taiwan, resulting in a significant positive net KE flux for mesoscale motions. The transfer around Suao Ridge is consistently downscaled with significant seasonal variation that is stronger in summer and weaker in winter. South of Suao Ridge, the transfer is one order of magnitude weaker and changes greatly with time. The cyclonic (anticyclonic) eddy weakens (enhances) KE transfer in most study areas. In particular, the cyclonic eddy reverses the transfer direction around Suao Ridge. The anticyclonic eddy triggers a significant bidirectional transfer south of Suao Ridge. Analyses show that the special arc-shaped topographic feature and northwestward Kuroshio intrusion current are responsible for the nature of bidirectional KE transfer northeast of Taiwan. The direction of mean current relative to the topography gradient determines the Rossby number magnitude and the KE transfer direction. The large-scale circulation determines the transfer intensity by changing the horizontal shear and barotropic instabilities. The KE transfer caused by nonlinear dynamics contributes significantly to the total anticyclonic eddy-induced net KE flux changes. In particular, the inverse KE cascade plays a key role in net KE flux changes in mesoscale motions east of Taiwan. Significance Statement In this work, we clarify the scale-to-scale kinetic energy transfer east of Taiwan. Energy transfer varies in different subareas. It is bidirectional northeast of Taiwan, consistently downscale around Suao Ridge, and weak and variable south of Suao Ridge. These transfer characteristics are closely related to the direction of mean flow relative to the topography gradient. Mesoscale eddies can trigger bidirectional transfer and even reverse the transfer direction. The reverse cascade is as important as the forward cascade for the total mesoscale energy change. This study not only shows an example of KE cascade when strong currents pass through continental slope, sea ridge, and open ocean, but also is of great significance for studying the dynamical and ecological environment variation of marginal sea.

The Processes and Relationships in Composers Scale

We introduce a new inventory labeled the Processes and Relationships in Composers Scale (PRCS). This is a novel inventory developed to self-assess creative and social factors inherent in music composition. The PRCS consists of two separate scales of 12 items each, namely the Composing Processes Scale (CPS) and the Social Relationship Scale (SRS). An exploratory factor analysis revealed that the CPS scale has a single factor structure, while the SRS scale relies on three main factors: loneliness, support, and friendship. The total score of the CPS was found to be highly reliable, whereas the SRS obtained a lower score. The PRCS can contribute new insights into how creative and social processes can be self-assessed by music composers with different backgrounds and levels of musical expertise. Our work aims to deepen understanding of the relationship between musical creativity and social life, contributing to existing scholarship that has explored this connection in musical activities specifically.

Academic Performance and Academic Self-Efficacy among Pre-University Students in Malaysia

This research investigated the relationship between academic performance and self-efficacy among pre-university students in Malaysia using cross-sectional survey data. The sample comprised 171 pre-university undergraduates, aged between 18 and 20, studying at a public university in Kuala Lumpur. They were derived from the population to form the sample using stratified random sampling. Two separate scales measuring academic self-efficacy and academic performance (i.e., the CEVEAPEU) were used to collect the survey data. The study used descriptive statistics, independent sample t-test, Pearson correlation, and multiple regression to analyze the data. The results indicate that a majority of the students reported a high level of academic self-efficacy and established a strong positive relationship between self-efficacy and academic performance. No statistically significant gender differences were found in the respondents’ academic self-efficacy, but academic performance was significantly influenced by academic self-efficacy. The findings suggest the potential involvement of additional variables, such as CGPA, in shaping students’ academic performance, highlighting the need for further exploration of these variables in future studies.

Effect of sinusoidal pulsating speed enhancement on the mixing performance of plastics machinery

Abstract Numerous vibration-assisted methods have been adopted to solve problems in polymer processing, but the introduction of vibration fields is typically done on small extruders or injectors in school laboratories and industrial research rooms, which profoundly limits the application of vibration technology. The purpose of this study is to put forward a simple vibration excitation method for all scale extruders or injection molding machines. To recover the mixing performance of that excitation method, a numerical investigation was carried out using the CFD software ANSYS POLYFLOW 19.2, and the analysis and comparison were made between the mixing performance of a simplified screw element with and without a sinusoidal pulsating speed field. The results showed that not all dynamic states with the superimposed excitation field have better mixing performance than the steady state without any pulsating field. Nevertheless, the introduction of a pulsating speed field under certain parameters setting can indeed enhance the stretching rate, reduce the separation scale, increase the mixing efficiency, and lower the screw force. These findings are of great importance and provide valuable references for the development and application of vibration-assisted molding technology in plastics machinery.

Characterization of very-large-scale motions in supersonic and hypersonic turbulent boundary layers

Very-large-scale motions are commonly observed in moderate- and high-Reynolds-number wall turbulence, constituting a considerable portion of the Reynolds stress and skin friction. This study aims to investigate the behaviour of these motions in high-speed and high-Reynolds-number turbulent boundary layers at varying Mach numbers. With the aid of high-precision numerical simulations, numerical experiments and theoretical analysis, it is demonstrated that the very-large-scale motions are weakened in high-Mach-number turbulence at the same friction Reynolds numbers, leading to the reduction in turbulent kinetic energy in the outer region. Conversely, the lower wall temperature enhances the very-large-scale motions but shortens the scale separation between the structures in the near-wall and outer regions.

P290 Evaluation of response to chronic and acute stress in patients with Crohn’s disease

Abstract Background Impaired response to stress in patients with chronic inflammatory disease, such as rheumatoid arthritis, is associated with decreased cortisol secretion. The aim of this study was the evaluation of response to chronic and acute stress in patients with Crohn’s Disease (CD). Methods Data was collected from patients who underwent surgery due to complications of Crohn’s (n=26)(CD group) or due to other indications (n=31) (control group). Patients on corticosteroid treatment during last 3 months and other immunological comorbidities were excluded. Cortisol concentration of the hair (proximal 3cm to the sculp) was measured as an indicative marker of stress taking place the last 3 months (chronic stress). Cortisol concentration in the saliva was measured at day 2 post surgery in a daily fluctuation manner (6 measurements in 24h), as an indicative marker of response to acute stress. The chemiluminescence method was used for cortisol measurements. Cortisol concentrations were correlated with DASS 21 questionnaire (validated Greek version),consisting of 21 questions which correspond to separate measurment scales for stress, anxiety or depression. SPSS was used for statistical analysis. Results Hair samples were measured from 17 CD patients and 20 controls. CD patients had significant lower concentrations of hair cortisol (median = 6.375 pgF/mg, IQR = 4.821 - 9.949) compared to control group (median = 9.643 pgF/mg, IQR = 6.602-14.637) (Mann-Whitney U-test P = 0.034). Saliva samples were measured from 21 CD patients and 27 controls. In regards to the post surgical cortisol fluctuation (acute stress), there was no significant difference between the two groups. No significant difference was observed between cortisol concentrations, and questionnaires results. Conclusion In CD, as in other immunological diseases, hypothalamic-pituitary–adrenal axis appears to be affected, leading in decreased response to chronic stress. This observation may have important implications for the pathophysiology, prognosis and treatment of CD.

A fully coupled regularized mortar‐type finite element approach for embedding one‐dimensional fibers into three‐dimensional fluid flow

SummaryThe present article proposes a partitioned Dirichlet‐Neumann algorithm, that allows to address unique challenges arising from a novel mixed‐dimensional coupling of very slender fibers embedded in fluid flow using a regularized mortar‐type finite element discretization. The fibers are modeled via one‐dimensional (1D) partial differential equations based on geometrically exact nonlinear beam theory, while the flow is described by the three‐dimensional (3D) incompressible Navier‐Stokes equations. The arising truly mixed‐dimensional 1D‐3D coupling scheme constitutes a novel approximate model and numerical strategy, that naturally necessitates specifically tailored solution schemes to ensure an accurate and efficient computational treatment. In particular, we present a strongly coupled partitioned solution algorithm based on a Quasi‐Newton method for applications involving fibers with high slenderness ratios that usually present a challenge with regard to the well‐known added mass effect. The influence of all employed algorithmic and numerical parameters, namely the applied acceleration technique, the employed constraint regularization parameter as well as shape functions, on efficiency and results of the solution procedure is studied through appropriate examples. Finally, the convergence of the two‐way coupled mixed‐dimensional problem solution under uniform mesh refinement is demonstrated, a comparison to a 3D reference solution is performed, and the method's capabilities in capturing flow phenomena at large geometric scale separation is illustrated by the example of a submersed vegetation canopy.

Trade‐Off Break between the Crystallinity and Phase Separation of Donor/Acceptor via a General Two‐Dimensional Transition‐Metal Phosphorus Trichalcogenides Nanoparticle Dopant Concept for Efficient and Stable All‐Polymer Solar Cells

All‐polymer solar cells (all‐PSCs) demonstrate splendid advantages of thermal and mechanical stability. Nevertheless, the rock‐ribbed trade‐off between the crystallinity and phase separation scale of donor/acceptor (D/A) hinder the power conversion efficiency (PCE) improvement of all‐PSCs. Here, a novel two‐dimensional transition‐metal phosphorus trichalcogenides (TMPTCs) namely Cd0.85PS3Li0.3 is intelligently designed and synthesized, and firstly employed as a nanoparticle dopant for PBDB‐T:N2200‐based all‐PSCs. The two‐dimensional Cd0.85PS3Li0.3 possess enormous surface area that can serve as the nucleation center, inducing the crystallinity of D/A without influencing the original phase separation. Such feature significantly boosted the charge transport, PCE (from 7.18% to 8.79%) and stability of PBDB‐T:N2200‐based device. Moreover, the Cd0.85PS3Li0.3 nanoparticle dopant was proved to be universal in non‐fullerene small molecule acceptor (NFSMA)‐based organic solar cells (OSCs), for which the PCE was boosted from 15.05% to 17.27% for PM6:L8‐BO‐based OSCs and from 17.29% to 19.10% for D18:L8‐BO‐based OSCs. These observations exemplify the significance of two‐dimensional TMPTCs nanoparticle dopant as a tool for breaking the rock‐ribbed trade‐off between the crystallinity and phase separation scale of D/A in OSCs, which may open up a special field for making two‐dimensional TMPTCs work in a unprecedented way in OSCs.

Impact of the numerical domain on turbulent flow statistics: scalings and considerations for canopy flows

Large eddy simulations (LES) are widely used to study the effects of surface morphology on turbulence statistics, exchange processes and turbulence topology in urban canopies. However, as LES are only approximations of reality, special attention is needed for the computational model set-up to ensure an accurate representation of the physical processes of interest. This paper shows that the choice of the numerical domain can significantly affect the accuracy of turbulent flow statistics, potentially causing a mismatch between numerical studies and experimental data. The study examines the influence of cross-stream aspect ratio (YAR), streamwise aspect ratio (XAR) and scale separation (SS) on first- and second-order flow statistics and turbulence topology. It is found that domains with a low YAR underestimate the velocity variance, while those with a low XAR overestimate the variance value. The study proposes a new approach based on the Buckingham Pi theorem to evaluate the effect of SS, as the existing method has major limitations for canopy flows. The results suggest that domains with small SS underpredict the variance value. To minimise the artificial impact of the numerical domain on turbulent flow statistics, the study recommends guidelines for future research, including a YAR of 3 or more, an XAR of 6 or more and an SS of 12 or more. Error tables are presented to allow researchers to select smaller domains than recommended, depending on their research interests in specific parts of the flow.

Dynamic H-Bond crosslinking strategy to prepare impact-hardening protective materials with tunable negative Poisson's ratio

Protective materials with a wide range of practical applications should exhibit a high energy absorption efficiency and be smart and stress-responsive. Herein, a novel smart protective material was formed from an impact-hardening polymer (IHP), which comprised a branched structure, and polyurethane (PU) with quadruple H-bonding. Notably, the quadruple H-bonding was used to enhance the interaction between the two microphases, thus regulating the negative Poisson's ratio. The value of the reversible softness–stiffness switching effect of this material (UPy-IHP-PU) achieved more than 5000, five times stronger than that of a previously reported linear IHP-PU. In addition, the impact-protective ability did not weaken. As the impact velocity increased, the impact energy absorption efficiency of UPy-IHP-PU also increased, even exceeded 70 % under the impact velocity of 5 m/s, thus demonstrating the ability to efficiently reduce the impact force and extend the buffer time against the strike via the impact-hardening phenomenon. Moreover, an adjustable scale of microphase separation can regulate the negative Poisson's ratio to enhance the impact-hardening phenomenon. The excellent energy dissipation ability and smart stress- and rate-responsiveness indicate the application potentials of UPy-IHP-PU as a future wearable impact-protective sensor.

Homogenization of a coupled electrical and mechanical bidomain model for the myocardium

We propose a coupled electrical and mechanical bidomain model for the myocardium tissue. The structure that we investigate possesses an elastic matrix with embedded cardiac myocytes. We are able to apply the asymptotic homogenization technique by exploiting the length scale separation that exists between the microscale where we see the individual myocytes and the overall size of the heart muscle. We derive the macroscale model which describes the electrical conductivity and elastic deformation of the myocardium driven by the existence of a Lorentz body force. The model comprises balance equations for the current densities and for the stresses, with the novel coefficients accounting for the difference in the electric potentials and elastic properties at different points in the microstructure. The novel coefficients of the model are to be computed by solving the periodic cell differential problems arising from application of the asymptotic homogenization technique. By combining both the mechanical and electrical behaviors, we obtain a macroscale model that highlights how the elastic deformation of the heart tissue is influenced and driven by the difference in the electric potentials at various points in the material.

Visualization and quantification of microphase separation in thermoplastic polyurethanes under different hard segment contents and its effect on the mechanical properties

The microstructure and macroscopic properties of thermoplastic polyurethanes (TPUs) are significantly affected by their microphase separation. It is therefore of great interest to quantitatively characterize the microphase separation of TPUs and explore its connection with their mechanical properties. In this work, a method based on atomic force microscopy is proposed to visualize and quantify the microphase separation of polyether TPUs with different hard segment contents. The lateral correlation length was proposed to describe the scale of microphase separation and the microscopic Young's modulus distributions were also obtained for comparison. Results show that the macroscopic Young's modulus of the polyether TPU is consistent with the microscopic Young's modulus only when the lateral correlation length reaches a certain threshold. Besides, the studied polyether TPU exhibits the best overall mechanical properties when it reaches the maximal lateral correlation length. The proposed AFM-based method demonstrates a versatile analytical tool for quantitatively assessing the microphase separation and unveiling the relationship between the microphase separation, microscopic mechanical properties, and the macroscopic properties of TPUs.

Determinants of Subjective Mental and Functional Health of Critical Illness Survivors: Comparing Pre-ICU and Post-ICU Status.

To compare ICU survivors' subjective mental and functional health before ICU admission and after discharge and to assess determinants of subjective health decline or improvement. Secondary analysis of the multicenter cluster-randomized Enhanced Recovery after Intensive Care trial ( ClinicalTrials.gov : NCT03671447). Ten ICU clusters in Germany. Eight hundred fifty-five patients with 1478 follow-up assessments. None. At two patient follow-ups scheduled 3 and 6 months after ICU discharge, patients rated their subjective mental and functional/physical health on two separate visual analog scales from 0 (worst) to 10 (best) in the previous week and before ICU admission. We compared pre-ICU and post-ICU subjective health and used mixed-effects regression to assess determinants of a health decline or improvement. At the first follow-up, 20% ( n = 165/841) and 30% ( n = 256/849) of patients reported a decline in subjective mental and functional health of at least three points, respectively; 16% ( n = 133/841 and n = 137/849) outlined improvements of mental and functional health. For 65% ( n = 543/841) and 54% ( n = 456/849), mental and functional health did not change three points or more at the first follow-up. Multivariable mixed-effects logistic regressions revealed that the ICU length of stay was a predictor of mental (adjusted odds ratio [OR] per ICU day, 1.04; 95% CI, 1.00-1.09; p = 0.038) and functional health (adjusted OR per ICU day, 1.06; 95% CI, 1.01-1.12; p = 0.026) decline. The odds of a mental health decline decreased with age (adjusted OR per year, 0.98; 95% CI, 0.96-0.99; p = 0.003) and the odds of a functional health decline decreased with time after discharge (adjusted OR per month, 0.86; 95% CI, 0.79-0.94; p = 0.001). The majority of ICU survivors did not experience substantial changes in their subjective health status, but patients with long ICU stays were prone to subjective mental and functional health decline. Hence, post-ICU care in post-ICU clinics could focus on these patients.