Boundary Fluctuations Research Articles

Covariant phase space formalism for fluctuating boundaries

We reconsider formulating D dimensional gauge theories, with the focus on the case of gravity theories, in spacetimes with boundaries. We extend covariant phase space formalism to the cases in which boundaries are allowed to fluctuate. We analyze the symplectic form, the freedoms (ambiguities), and its conservation for this case. We show that boundary fluctuations render all the surface charges integrable. We study the algebra of charges and its central extensions, charge conservation, and fluxes. We briefly comment on memory effects and questions regarding semiclassical aspects of black holes in the fluctuating boundary setup.

An analysis of the suppression of a pair of odd and even temperature fluctuation in an area occupied by a two-phase one-directional periodically layered composite

The study concerns a heat conduction problem in a two-phase, one-directional periodically layered composite (commonly referred to as a laminate). The model is strictly related to considerations regarding continuous media and was introduced by Professor Czesław Woźniak. The basis for the study is a re-formulation of the heat conduction model for composites, referred to in the literature as the extended tolerance heat conduction model. The model equations consider coefficients responsible for the intensity of exponential and rotational suppression of boundary fluctuations of a temperature field in a limited area or in a half-space occupied by the composite. The study investigated the dependence of the suppression intensity of boundary fluctuations on the geometrical and material properties of the composite. Three special cases of pairs of interacting boundary fluctuations were analysed.

Experiment and Simulation on the Ferrofluid Boundary Deformation and Fluctuation Characters of a High-Speed Rotary Seal

Abstract A ferrofluid seal is a rotary seal widely used in the chemical industry, shipbuilding, aerospace, aviation, and other fields, demonstrating various advantages, such as high reliability, low wear, and low leakage rate. The reason for sealing is that the ferrofluid ring isolates the sealed gas from the atmosphere. Hence, boundary deformation and fluctuation are two significant factors to consider for the design of a ferrofluid seal. However, the ferrofluid boundary is wrapped in the shell and pole shoe, which poses a challenge in direct observation. In this paper, an experimental ferrofluid rotary seal device is presented, which can be used to monitor the boundary changes at different rotational speeds and pressure differences. According to the simulation result, the boundary fluctuation affects the pressure transfer and causes the sealing performance to deteriorate. The ferrofluid boundary obtained through the experiment is essential for an in-depth investigation into the rotary seal failure mechanism for improving the design of the ferrofluid rotary seal.

Adaptive penalty method with adam optimizer for enhanced convergence in optical waveguide mode solvers.

We propose a cutting-edge penalty method for optical waveguide mode solvers, integrating the Adam optimizer into pseudospectral frequency-domain (PSFD) frameworks. This strategy enables adaptable boundary fluctuations at material interfaces, significantly enhancing numerical convergence and stability. The Adam optimizer, an adaptive algorithm, is deployed to determine the penalty coefficient, greatly improving convergence rates and robustness while effectively incorporating boundary conditions into the interfaces of subdomains. Our solver evaluates the numerical performance of optical waveguides by calculating effective indices of standard benchmark waveguides with high accuracy. This method diminishes numerical boundary errors and provides a marked increase in convergence speed and superior accuracy when compared to conventional methods and even metaheuristic optimization methods, all while maintaining the inherent global spectral accuracy of the PSFD.

A black hole toy model with non-local and boundary modes from non-trivial boundary conditions

We study gauge theories between two parallel boundaries with non-trivial boundary conditions, which serve as a toy model for black hole background with two boundaries near the horizon and infinite, aiming for a better understanding of the Bekenstein–Hawking entropy. The new set of boundary conditions allows boundary modes and non-local modes that interplay between the two boundaries. Those boundary modes and Wilson lines stretched between the two boundaries are carefully analyzed and are confirmed as physical variables in the phase space. Along with bulk fluctuation modes and topological modes, the partition function and entropy of all physical modes are evaluated via Euclidean path integral. It is shown that there are transitions between the dominance of different modes as we vary the temperature. The boundary fluctuation modes whose entropy is proportional to the volume dominate at high temperatures, and the boundary-area scaled boundary modes and Wilson lines are the more important at low temperatures. At super-low temperatures, when all the fluctuation modes die off, we see the topological modes whose entropy is the logarithm of the length scales of the system. The boundary modes and non-local modes should have their counterparts in a black hole system with similar boundary conditions, which might provide important hints for black hole physics.

On flow close to cavern boundaries in yield stress fluids - revisited. Current interpretation

About 30 years ago, Professor Alvin W. Nienow co-authored an experimental paper which reported slow motion of tracer particles, both close inside and outside of a cavern boundary formed in stirred Carbopol 940 microgel, however no theoretical explanation of the motion outside the cavern was given. Here, the motion of the particles outside the cavern was explained based on current knowledge, supported by rheological measurements and CFD modelling. According to current understanding of the yield stress fluids and the results of numerical simulation, the flow outside the cavern can result from presence of slip velocity of solid microgel at vessel wall and/or from periodic radial fluctuations of cavern boundaries during rotation.

Marine bioturbation collapse during Early Jurassic deoxygenation: implications for post-extinction marine ecosystem functioning

Abstract Climate change is undermining the health and integrity of seafloor ecosystems, with declines in bioturbation expected to impact future ecosystem functioning. We explored changes in the nature and degree of bioturbation during Early Jurassic global warming and ocean deoxygenation. Understanding how these communities responded can help anticipate how bioturbation and ecosystem functioning might change over large spatial and temporal scales. Trace and body fossils from outcrop and core in the Cleveland Basin, UK show how healthy seafloor communities deteriorated through the Pliensbachian spinatum Zone, and macroinfaunal behaviour fluctuated across the Pliensbachian–Toarcian boundary coincident with mass extinction. Deoxygenation began above the stage boundary, and conditions deteriorated until bioturbation ceased completely (upper tenuicostatum Zone) for 0.6–2.5 Ma, longer than anywhere else in NW Tethys. The macroinfaunal record revealed new details on the progression and timing of deoxygenation, benthic recovery and fluctuations in the palaeoredox boundary. After the oceanic anoxic event infauna were fewer, smaller and did not mix sediments to depth, and while the depth and diversity of bioturbation had increased by the fibulatum Subzone ( bifrons Zone), the benthos had not recovered to late Pliensbachian pre-oceanic anoxic event state. Bioturbation collapse over large parts of the Northern Hemisphere probably contributed to regional-scale changes in ecosystem functioning.

Homogenization for stochastic Ginzburg-Landau equation on the half-line with fast boundary fluctuation

In this paper, we investigate the homogenization for complex stochastic Ginzburg-Landau equation on the half-line with fast boundary fluctuation. Precisely, we first verify the existence and uniqueness of the mild solution to the initial-boundary problem in a weighted space. Next, we discuss the tightness of the mild solution. Finally, we prove that the mild solution of the original system converges to the mild solution of the homogenized equation in probability, as ε goes to zero.

Transient thermal rectification effect of one-dimensional heterostructure

Like an electric diode, thermal diode transmits heat in a specific direction, and thermal rectification is also a fundamental phenomenon for active heat flow control. However, in practical applications, thermal rectification needs to be operated under transient conditions. In this study, transient thermal rectification ratio of a one-dimensional heterostructure is numerically investigated by using the finite element method. The effects of interface thermal resistance, interface initial gap, periodic boundary condition and geometric and material parameters on the transient thermal resistance ratio are obtained. Research indicates that the interface thermal resistance can enhance the thermal rectification effect of the system, and the introduction of the initial interface gap improves the transient thermal rectification ratio by an order of magnitude. The ability to engineer the thermal diffusivity of materials allows us to control the heat flux and improve transient thermal rectification ratio. Since interface thermal resistance can enlarge the difference in heat transfer capability between forward case and reverse case, it is reasonable to suggest that adjusting the interface thermal resistance may also enhance the thermal rectification effect, but excessive interface thermal resistance will reduce it. Under the periodic temperature boundary conditions, the larger the temperature difference in boundary fluctuation, the larger the fluctuation amplitude of the transient thermal rectification ratio is. The fluctuation frequency of thermal rectification changes with the periodic boundary frequency, which also affects the amplitude of the fluctuation. Furthermore, by adjusting the initial interface gap, the gap is closed during heat transfer and the interface thermal resistance is reduced in the forward case, while the interface gap is kept open in the reverse case, thereby improving the overall thermal rectification ratio by an order of magnitude. For different transient stages, the equivalent thermal conductivity can be changed by adjusting the material and geometrical properties to improve the thermal rectification ratio.Therefore, the proposed numerical approach and results can guide the optimal design of the transient thermal rectifier.

Fracton critical point at a higher-order topological phase transition

The theory of quantum phase transitions separating different phases with distinct symmetry patterns at zero temperature is one of the foundations of modern quantum many-body physics. Here we demonstrate that the existence of a two-dimensional topological phase transition between a higher-order topological insulator (HOTI) and a trivial Mott insulator with the same symmetry eludes this paradigm. We present a theory of this quantum critical point (QCP) driven by the fluctuations and percolation of the domain walls between a HOTI and a trivial Mott insulator region. Due to the spinon zero modes that decorate the rough corners of the domain walls, the fluctuations of the phase boundaries trigger a spinon-dipole hopping term with fracton dynamics. Hence we find that the QCP is characterized by a critical dipole liquid theory with subsystem U(1) symmetry and the breakdown of the area law entanglement entropy which exhibits a logarithmic enhancement: $Lln(L)$. Using the density matrix renormalization group method, we analyze the dipole stiffness together with the structure factor at the QCP, which provides strong evidence of a critical dipole liquid with a Bose surface, UV-IR mixing, and a dispersion relation $\ensuremath{\omega}={k}_{x}{k}_{y}.$

Spontaneous multi-scale void formation and closure in densifying epithelial and fibroblast monolayers from the sub-confluent state.

Using time-lapse phase contrast microscopy, the formation and closure of spontaneously generated voids in the densifying monolayers of isotropic epithelial cells (ECs) and elongated fibroblast cells (FCs) through proliferation from the sub-confluent state are investigated. It is found that, in both types of monolayers after forming a connected network composed of nematic patches with different orientations, numerous multi-scale voids can be spontaneously formed and gradually close with increasing time. The isotropic fluctuations of deformation and crawling of ECs and the anisotropic axial motion/alignment polarizations of FCs are the two keys leading to the following different generic dynamical behaviors. In EC monolayers, voids exhibit irregular boundary fluctuations and easier cell re-orientation of front layer cells (FLCs) surrounding void boundaries. Void closures are mainly through pinching the gap between the opposite fluctuating void boundaries, and the inward crawling of FLCs to reduce void area associated with topological rearrangement to reduce FLC number. In FC monolayers, large voids have piecewise smooth convex boundaries, and cusp-shaped concave boundaries with cells orienting toward the void at cusp tips. The extension of a thin cell bridge from the cusp tip can bisect a large void into smaller voids. For smaller FC voids dominated by convex boundaries, along which cell alignment prohibits inward crawling, the reduction of FLC number through successive outward squeezing of single FLCs by neighboring FLCs sliding along the void boundary plays an important role for topological rearrangement and void closure. Unlike those surrounding artificial wounds in dense EC monolayers, the absence of ring-like purse-strings surrounding EC and FC voids allows topological rearrangements for reducing void perimeter and void area.

3D field data of flow structures in dead-ended, coolant loop reactor branch lines for CFD validation of thermal fatigue onset modeling

Thermal fatigue phenomena in normally stagnant branch lines connected to the primary loop of pressurized water reactors has been identified as a primary cause for at least ten pipe cracking events in the past decade. Current prediction and inspection of at-risk piping is based on semi-empirical models, derived on the basis of low-resolution experimental data. This data does not include sufficient information on contributing factors that lead to thermal boundary development and fluctuation in dead-ended branch lines. Without comprehensive, high-resolution data of the phenomena involved, CFD models attempting to account for the re-laminarization or quasi-laminar flow that persists in the branch line cannot be validated.Validated CFD models for dead-ended branch line flow conditions will greatly expand the predictive capabilities the method currently offers. To build the database necessary for related CFD validation campaigns, 3D high-resolution measurements were made in the branch line of an experimental facility built at the University of Michigan. The facility is a scaled coolant flow loop with a reduced main line diameter. Nuclear power plant coolant loop flow rates near 10 m/s were achieved for study. High-resolution, 3D velocity field data in the dead-ended branch line was obtained using Tomographic Particle Image Velocimetry (T-PIV) techniques. With this data as a basis for validation, CFD models such as Low-Re will be able to accurately predict flow phenomena in dead-ended branch line simulations where the branch line diameter, opening geometry, or piping component (elbow) locations are altered.

Preliminary measurements of transient boundary heat transfer process under supercritical pressures using pixelated phase-shifting interferometry

The boundary heat transfer dynamics of supercritical carbon dioxide (CO2) is vital to its application in solar heater, extraction, refrigeration, heat pumps, power generations, nuclear systems and many other occasions. In this study, an experiment system using pixelated-array masked phase-shifting interferometer has been established for the visualization of temperature of supercritical CO2. The laser diagnostic process has been operated with a carefully designed visualization chamber to give clear transient results of the density and temperature fields for the first time. Those field information has been used to calculate the heat transfer characteristic parameters of the supercritical CO2 fluid in different boundary conditions. The current quantitative visualization analysis by the utilization of pixelated methods is shown capable of giving transient analysis of detailed field evolutions. The results show that (1) small temperature differences are generated in supercritical boundary due to the typical large thermal capacity; (2) supercritical convection boundary is with much quicker thermal quenching than subcritical states, while the subcritical states boundary parameter show localized characteristics while supercritical cases show fluctuation phenomena; (3) the boundary fluctuations heat transfer field exist for supercritical states and the fluctuations affect the overall heat transfer behaviour and the field evolution in supercritical states.

Unified method for measuring entropy differences between coexisting surface phases using low energy electron microscopy

We demonstrate the ability of low energy electron microscopy (LEEM) to extract fundamental information in surface phase transitions during in situ observations of complex semiconductor surfaces. We utilize established LEEM techniques and develop a methodology that enables us to calculate the surface entropy difference using only LEEM measurements without the need for external characterization. We demonstrate the effectiveness of the unified method by monitoring the phase coexistence during the first-order transition between the $c\phantom{\rule{0.16em}{0ex}}(8\ifmmode\times\else\texttimes\fi{}2)$ and $(6\ifmmode\times\else\texttimes\fi{}6)$ phases on the surface of GaAs(001) at a range of temperatures relevant for epitaxy. The coexistence behavior with temperature and the fluctuations of phase boundaries are measured and analyzed to obtain the entropy difference and stress difference between the phases. The calculated values show that the entropy difference is not large enough to stabilize the $(6\ifmmode\times\else\texttimes\fi{}6)$ phase with respect to the $c\phantom{\rule{0.16em}{0ex}}(8\ifmmode\times\else\texttimes\fi{}2)$ by itself, suggesting that the elastic relaxation during the coexistence between the two phases is necessary to stabilize the $(6\ifmmode\times\else\texttimes\fi{}6)$ phase.

Control of Line Tension at Phase-Separated Lipid Domain Boundaries: Monounsaturated Fatty Acids with Different Chain Lengths and Osmotic Pressure.

Line tension at phase-separated lipid domain boundaries is an important factor that governs the stability of the phase separation. We studied the control of the line tension in lipid membranes composed of dioleoylphosphocholine (DOPC), dipalmitoylphosphocholine (DPPC), and cholesterol (Chol) by the addition of the following three monounsaturated fatty acids (MUFAs) with different chain lengths: palmitoleic acid (PaA), oleic acid (OA), and eicosenoic acid (EiA). In addition, we attempted to alter the line tension by applying osmotic pressure. The phase behavior of the MUFA-containing lipid membranes in the presence and absence of osmotic stress was observed by fluorescence and confocal laser scanning microscopy. The line tension was quantitatively measured from the domain boundary fluctuation by flicker spectroscopy, and the interactions between the lipids and MUFAs were examined by differential scanning calorimetry. PaA and OA, which are shorter MUFAs, decreased the line tension, whereas EiA changed the liquid domain to a solid domain. The osmotic pressure increased the line tension, even in the presence of MUFAs. It may be possible to control the line tension by combining the chemical approach of MUFA addition and the physical approach of applying osmotic pressure.

Kelvin-Helmholtz Vortices as an Interplay of Magnetosphere-Ionosphere Coupling

The solar wind-magnetosphere interaction drives diverse physical processes on the flanks of Earth’s magnetopause, and in turn these processes couple to the ionosphere. We investigate simultaneous multipoint in-situ spacecraft and ground-based measurements to determine the role of Kelvin-Helmholtz waves at the Earth’s magnetopause and the low-latitude boundary layer in the magnetosphere-ionosphere coupling process. Nonlinear Kelvin-Helmholtz waves develop into flow vortices that twist and/or shear flux tube magnetic fields, thereby generating localized field-aligned currents. Kelvin-Helmholtz vortices on the dusk (dawn) flanks of the magnetosphere generate clockwise (counter-clockwise) rotations and upward (downward) field-aligned currents inside the flux tubes, consistent with the region-1 field-aligned current. We present in-situ MMS and Cluster spacecraft observations of Kelvin-Helmholtz vortices at the magnetopause that map to the poleward edge of the auroral regions. The FAST spacecraft and the ground-based magnetometers from which spherical elementary currents (acting as a proxy for vertical currents) can be calculated observe corresponding field-aligned current signatures. This study demonstrates the role played by the Kelvin-Helmholtz waves in linking magnetopause boundary fluctuations to ionospheric phenomena.

Boundary fluctuation dynamics of a phase-separated domain in planar geometry.

Using phase-ordering kinetics and of renormalization group theories, we derive analytically the relaxation times of the long wavelength fluctuations of a phase-separated domain boundary in the vicinity of (and below) the critical temperature in the planar Ising universality class. For a conserved order parameter, the relaxation time grows like Λ^{3} at wavelength Λ and can be expressed in terms of parameters relevant at the microscopic scale: lattice spacing, bulk diffusion coefficient of the minority phase, and temperature. These results are supported by numerical simulations of 2D Ising models, enabling in addition calculating the nonuniversal numerical prefactor. We discuss the applications of these findings to the determination of the real timescale associated with elementary Monte Carlo moves from the measurement of long wavelength relaxation times on experimental systems or molecular dynamics simulations.

A Hybrid Multi-Objective Particle Swarm Optimization with Central Control Strategy

In recent years, researchers have solved the multi-objective optimization problem by making various improvements to the multi-objective particle swarm optimization algorithm. However, we propose a hybrid multi-objective particle swarm optimization (CCHMOPSO) with a central control strategy. In this algorithm, a disturbance strategy based on boundary fluctuations is first used for the updated new particles and nondominant particles. To prevent the population from falling into a local extremum, some particles are disturbed. Then, when the external archive capacity reaches the extreme value, we use a central control strategy to update the external archive, so that the archive solution gets a good distribution. When the dominance of the current particle and the individual best particle cannot be determined, to enhance the diversity of the population, the combination method of the current particle and the individual best particle can be used to update the individual best particle. The experimental results show that CCHMOPSO is better than four multi-objective particle swarm optimization algorithms and four multi-objective evolutionary algorithms. It is a feasible method for solving multi-objective optimization problems.

Critical phase boundary and finite-size fluctuations in the Su-Schrieffer-Heeger model with random intercell couplings

A dimerized fermion chain, described by Su-Schrieffer-Heeger (SSH) model, is a well-known example of 1D system with a non-trivial band topology. An interplay of disorder and topological ordering in the SSH model is of a great interest owing to experimental advancements in synthesized quantum simulators. In this work, we investigate a special sort of a disorder when inter-cell hopping amplitudes are random. Using a definition for $\mathbb{Z}_2$-topological invariant $\nu\in \{ 0; 1\}$ in terms of a non-Hermitian part of the total Hamiltonian, we calculate $\langle\nu\rangle$ averaged by random realizations. This allows to find (i) an analytical form of the critical surface that separates phases of distinct topological orders and (ii) finite size fluctuations of $\nu$ for arbitrary disorder strength. Numerical simulations of the edge modes formation and gap suppression at the transition are provided for finite-size system. In the end, we discuss a band-touching condition derived within the averaged Green function method for a thermodynamic limit.

Lattice-based Monte Carlo simulation of the effects of nutrient concentration and magnetic field exposure on yeast colony growth and morphology.

Yeasts exist in communities that expand over space and time to form complex structures and patterns. We developed a lattice-based framework to perform spatial-temporal Monte Carlo simulations of budding yeast colonies exposed to different nutrient and magnetic field conditions. The budding patterns of haploid and diploid yeast cells were incorporated into the framework, as well as the filamentous growth that occurs in yeast colonies under nutrient limiting conditions. Simulation of the framework predicted that magnetic fields decrease colony growth rate, solidity, and roundness. Magnetic field simulations further predicted that colony elongation and boundary fluctuations increase in a nutrient- and ploidy-dependent manner. These in-silico predictions are an important step towards understanding the effects of the physico-chemical environment on microbial colonies and for informing bioelectromagnetic experiments on yeast colony biofilms and fungal pathogens.