Hard Wall Research Articles

A comparative ultrastructural study of tintinnid loricae (Alveolata, Ciliophora, Spirotricha) and a hypothesis on their evolution.

Tintinnid ciliates build loricae, whose structure, shape, and size still largely represent the basis for taxonomy and classification, although genetic analyses demonstrated their limited utility for inferring evolutionary relationships. The textures of the lorica walls, however, result from the chemical and physical properties of the forming material, which is supposed to be rather conserved in closely related taxa, viz., congeners and confamilial genera. Within a particular texture, small deviations in the chemical composition might affect the wall's stickiness and accordingly its capability to adhere foreign particles, explaining the intertwining of tintinnids with hyaline and agglutinated loricae in phylogenetic inferences. In a comprehensive comparative study, the lorica textures were electron microscopically and morphometrically analyzed in 21species from 17genera and more than nine families together with literature data. Most species were investigated for the first time, and the taxa cover a substantial portion of the molecular genealogy. The phylogeny-aware analysis of the lorica-related features provides a preliminary hypothesis on lorica evolution. Eventually, this conspectus suggests the dominance of hard lorica walls with an alveolar texture and proposes different modes of lorica formation.

The depletion thickness in solutions of semi-flexible polymers near colloidal surfaces: analytical approximations.

We derive a simple, yet accurate approximate mean-field expression for the depletion thickness δsf of a solution of dilute semi-flexible polymers next to a hard surface. In the case of a hard wall this equation has the simple form δsf = δ0[1 − tanh(psf/δ0)], where psf accounts for the degree of flexibility and δ0 is the depletion thickness in the case of fully flexible polymers. For fixed polymer coil size, increasing the chain stiffness leads to a decrease in the depletion thickness. The approach is also extended to include higher polymer concentrations in the semidilute regime. The analytical expressions are in quantitative agreement with numerical self-consistent field computations. A remarkable finding is that there is a maximum in the depletion thickness as a function of the chain stiffness in the semidilute concentration regime. This also means that depletion attractions between colloidal particles reach a maximum for a certain chain stiffness, which may have important implications for the phase stability of colloid–polymer mixtures. The derived equations could be useful for the description of interactions in- and phase stability of mixtures of colloids and semi-flexible polymers.

Configuration entropy and confinement-deconfinement transition in higher-dimensional hard wall model

We consider a higher-dimensional hard wall model with an infrared (IR) cut-off in asymptotically AdS space and investigate its thermodynamics via the holographic renormalization method. We find a relation between the confinement temperature and the IR cut-off for any dimension. It is also shown that the entropy of p-branes with the number of coincident branes (the number of the gauge group) N jumps from leading order in O(N0) at the confining low temperature phase to O(Np+12) at the deconfining high temperature phase like D3-branes (p=3) case. On the other hand, we calculate the configuration entropy (CE) of various magnitudes of an inverse temperature at an given IR cut-off scale. It is shown that as the inverse temperature grows up, the CE above the critical temperature decreases and AdS black hole (BH) is stable while it below the critical temperature is constant and thermal AdS (ThAdS) is stable. In particular, we also find that the CE below the critical temperature becomes constant and its magnitude increases as a dimension of AdS space increases.

Study of fluid layer gravity motion over vertical surface

This paper presents the results of studying the motion of a liquid layer along the walls of a vertically installed pipe under the action of gravity. Two-dimensional boundary layer is formed by the fluid motion relative to the hard wall on surfaces of structures (pipes, turbines, heat-and-mass transfer equipment, aircrafts, ships, etc.), which are of positive interest in engineering practice. Further upgrading of the above-mentioned structures is possible only by increasing accuracy of momentum in the boundary layer, heat and mass transfer rates calculation. It is confirmed that in the boundary layer transfer phenomena intensity (perpendicular to the wall) is due to the fluid particles velocity distribution regularities in the cross-section of the layer. Fluid velocity distribution regularities in turn are conditioned by Reynolds number according to current notions. The principal method of quantitative analysis of turbulent flow in a boundary layer suggested by Reynolds continues to be the velocity and pressure fluctuations averaging method for some timespan. The suggested model of fluid movement enables to prognosticate conditions under which in cross-sections of the boundary layer reshaping of velocity profile takes place, to carry out analytic calculation of such hydrodynamic characteristics as mean velocity of motion, layer thickness and shearing stresses acting on the wall. The difference between the suggested methods developed for calculation of flow parameters from the well-known ones is in that that calculations are made based on an integrated approach regardless of such conceptual definitions as laminar and turbulent regimes widely used in modern hydrodynamics. Obtained results and design formulas known in the literature have been compared. It has been found that the thickness of the sliding layer, determine by the proposed calculation formula, 1.17 times smaller than that determined by the currently used formula

Hard-wall edge confinement in two-dimensional topological insulators and the energy of the Dirac point

In 2D topological insulators (TIs) based on semiconductor quantum wells such as HgTe/CdTe, hard wall spin-polarized edge states are calculated from an $8\ifmmode\times\else\texttimes\fi{}8$ linear-$k$ multiband (LKMB) Hamiltonian based directly on $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ theory, and from a $4\ifmmode\times\else\texttimes\fi{}4$ BHZ Hamiltonian derived from it by the elimination of remote states using perturbation theory. Both approaches lead to similar results with standard boundary conditions obtained by integrating the eigenstate equation across an interface (SBCs). In contrast, open boundary conditions (OBCs) yield unphysical results and do not work for the LKMB Hamiltonian. Their failure is traced to a spurious solution introduced by the elimination process. In the BHZ treatment, SBCs are shown to be consistent with perturbation theory on both sides of the boundary, and a wall hybridization parameter is estimated for a vacuum using a basis of empty crystal free electron states. A Dirac point is not expected for a vacuum, but can exist when a thin passivation layer is used whose midgap energy is nearly degenerate with that of the TI. In the absence of interface band mixing (IBM), the Dirac point is then very close to midgap and virtually independent of the TI band asymmetry. IBM introduces a significant energy shift, which decreases monotonically with edge state wave vector. Using SBCs, the paradoxical extension of the BHZ edge states across the topological phase transition is also resolved.

A DECEITFUL RIGHT ATRIAL MASS.

This large atrial mass was removed from a 33-yearold patient admitted to the emergency department for severe venous congestion. Its hard texture, grayish discolouration and wall infiltration prompted radical excision and partial atrial reconstruction. Histopathology was compatible with a thrombus, discarding malignancy.

Edge Behavior of Two-Dimensional Coulomb Gases Near a Hard Wall

We consider a two-dimensional determinantal Coulomb gas confined by a class of radial external potentials. In the limit of large number of particles, the Coulomb particles tend to accumulate on a compact set S, the support of the equilibrium measure associated with a given external potential. If the particles are forced to be completely confined in a disk \({\mathcal {D}}\) due to a hard-wall constraint on \({\partial }{\mathcal {D}}\subset {\text {Int}}S\), then the equilibrium configuration changes and the equilibrium measure acquires a singular component at the hard wall. We study the local statistics of Coulomb particles in the vicinity of the hard wall and prove that their local correlations are expressed in terms of “Laplace-type” integrals, which appear in the context of truncated unitary matrices in the regime of weak non-unitarity.

Monte Carlo Simulations of Biaxial Molecules Near Hard Wall

A system of optimal biaxial molecules placed at the sites of a cubic lattice is studied in an extended Lebwohl-Lasher model. Molecules interact only with their nearest neighbors through the pair potential that depends on the molecule orientations. It is known that in the homogeneous system there is a direct second-order transition from the isotropic to the biaxial nematic phase, but properties of confined systems are less known. In the present paper the lattice has periodic boundary conditions in the X and Y directions and it has two walls with planar anchoring, perpendicular to the Z direction. We have investigated the model using Monte Carlo simulations on $N_x \times N_y \times N_z$ lattices, $N_x = N_y = 10, 16$, $N_z$ from 3 to 19, with and without assuming mirror symmetry. This study is complementary to the statistical description of hard spheroplatelets near a hard wall by Kapanowski and Abram [Phys. Rev. E 89, 062503 (2014)]. The temperature dependence of the order-parameter profiles between walls is calculated for many wall separations. For large wall separations there are the surface layers with biaxial ordering at both walls (4-5 lattice constants wide) and beyond the surface layers the order parameters have values as in the homogeneous system. For small wall separations the isotropic-biaxial transition is shifted and the surface layers are thinner. Above the isotropic-biaxial transition the preferable orientations in both surface layers can be different. It is interesting that planar anchoring for biaxial molecules leads to the uniaxial interactions at the wall. As a result we get the planar Lebwohl-Lasher model with additional (biaxial) interactions with the neighbors from the second layer, where the Kosterlitz-Thouless transition is present.

Universal properties of boundary and interface charges in continuum models of one-dimensional insulators

We study single-channel continuum models of one-dimensional insulators induced by periodic potential modulations which are either terminated by a hard wall (the boundary model) or feature a single region of dislocations and/or impurity potentials breaking translational invariance (the interface model). We investigate the universal properties of excess charges accumulated near the boundary and the interface, respectively. We find a rigorous analytic proof for the earlier observed linear dependence of the boundary charge on the phase of the periodic potential modulation as well as extend these results to the interface model. The linear dependence on the phase shows a universal value for the slope, and is intersected by discontinuous jumps by plus or minus one electron charge at the phase points where localized states enter or leave a band of extended states. Both contributions add up such that the periodicity of the excess charge in the phase over a $2\pi$-cycle is maintained. While in the boundary model this property is usually associated with the bulk-boundary correspondence, in the interface model a correspondence of scattering state and localized state contributions to the total interface charge is unveiled on the basis of the so-called nearsightedness principle.

Harmonically confined long-ranged interacting gas in the presence of a hard wall

In this paper, we compute exactly the average density of a harmonically confined Riesz gas of N particles for large N in the presence of a hard wall. In this Riesz gas, the particles repel each other via a pairwise interaction that behaves as |x i − x j |−k for k > −2, with x i denoting the position of the ith particle. This density can be classified into three different regimes of k. For k ⩾ 1, where the interactions are effectively short-ranged, the appropriately scaled density has a finite support over [−l k (w), w] where w is the scaled position of the wall. While the density vanishes at the left edge of the support, it approaches a nonzero constant at the right edge w. For −1 < k < 1, where the interactions are weakly long-ranged, we find that the scaled density is again supported over [−l k (w), w]. While it still vanishes at the left edge of the support, it diverges at the right edge w algebraically with an exponent (k − 1)/2. For −2 < k < −1, the interactions are strongly long-ranged that leads to a rather exotic density profile with an extended bulk part and a delta-peak at the wall, separated by a hole in between. Exactly at k = −1 the hole disappears. For −2 < k < −1, we find an interesting first-order phase transition when the scaled position of the wall decreases through a critical value w = w*(k). For w < w*(k), the density is a pure delta-peak located at the wall. The amplitude of the delta-peak plays the role of an order parameter which jumps to the value 1 as w is decreased through w*(k). Our analytical results are in very good agreement with our Monte-Carlo simulations.

Strong-coupling corrections to hard domain walls in superfluid He3−B

Domain walls in superfluid $^{3}\mathrm{He}\text{\ensuremath{-}}B$ have gained renewed interest in light of experimental progress on confining helium in nanofabricated geometries. Here, we study the effect of strong-coupling corrections on domain wall width and interfacial tension by determining self-consistent solutions to spatially-dependent Ginzburg-Landau equations. We find that the formation of domain walls is generally energetically favored in strong coupling over weak coupling. Calculations were performed over a wide range of temperatures and pressures, showing decreasing interface energy with increasing temperature and pressure. This has implications for the observability of such domain walls in $^{3}\mathrm{He}\text{\ensuremath{-}}B$, which are of both fundamental interest and form the basis for spatially-modulated pair-density wave states, when stabilized by strong confinement.

Neutrino-nucleon DIS from holographic QCD: PDFs of sea and valence quarks, form factors, and structure functions of the proton

We discuss unpolarized neutrino- and anti-neutrino-nucleon deep inelastic scattering using a chiral doublet of baryonic sources with explicit symmetry breaking, in a slice of ${\mathrm{AdS}}_{5}$ with both a hard and soft wall. We explicitly derive the direct and transition form factors for the vector and axial-vector currents for the holographic dual of a proton and neutron. We use them to derive the $s$-channel structure functions for neutrino and antineutrino scattering on a proton and neutron in bulk. The $t$-channel contributions stemming from the Pomeron and Reggeon exchanges are also evaluated explicitly. The pertinent even and odd structure functions in the limit of large and small parton momentum fraction $x$ are given. The results allow for the extraction of the nonperturbative parton distribution functions carried by the sea and valence quarks both at large-$x$ and small-$x$ regimes. Our holographic parton distribution function (PDF) sets compare well with the Les Houches accord PDF (LHAPDF) and the coordinated theoretical-experiment project on QCD (CTEQ) PDF sets in the large-$x$ and small-$x$ regimes in the intermediate range of ${Q}^{2}&lt;10\text{ }\text{ }{\mathrm{GeV}}^{2}$.

Long-range oscillations of a single-particle distribution function for a molecular system of hard spheres near a solid surface in the Percus–Yevick approximation

The properties of molecular systems are defined by asymptotic behavior of distribution functions that have descending character with long-range oscillating order. We consider the molecular system of hard spheres near hard wall. The decrement and period of oscillation are calculated for the distribution function which defines the local density profile.

Experimental and Numerical Analysis of Sunroof Buffeting of a Simplified Mercedes-Benz S-Class

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Sunroof buffeting is examined experimentally and numerically in this paper. Despite the fact that some consider the simulation process for sunroof buffeting to be mature, there remain substantial uncertainties even in recently published methodologies. Capturing the frequencies and especially the sound pressure levels correctly is essential if CFD simulations are intended to be used during early stages of a car development process. Numerous experimental results of sunroof buffeting and the interior low-frequency characteristics of a 2013 Mercedes-Benz S-Class have been used to develop a simplified car model: a full-size S-Class model with slightly simplified geometries in the interior as well as at the exterior. To avoid the effects of numerous different materials in the interior, it is solely made from polyurethane and aluminum and built to maximize its structural rigidity and air-tightness. The air-tightness of the cabin and structural modes of body parts have the greatest impact on the Helmholtz frequencies, which are excited by the vortex shedding in the sunroof opening.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;With this simplified car model various measurements are carried out to validate the numerical simulation method. The measurement data consists of acoustic data as well as flow quantities. In this paper, Star-CCM+ is used to conduct improved delayed detached eddy simulations with direct noise calculation in order to predict the buffeting frequencies that occur at different wind speeds correctly. Due to the rigid and acoustically hard walls of the simplified car model, which fairly match the numerical boundary conditions, it is possible to predict the interior sound pressure levels correctly as well.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;The presented results demonstrate that state-of-the-art CFD codes are capable of predicting sunroof buffeting frequencies and noise levels correctly if the experimental and numerical boundary conditions match.&lt;/div&gt;&lt;/div&gt;

Comment on “Kosterlitz-Thouless-type caging-uncaging transition in a quasi-one-dimensional hard disk system”

Huerta et al. [Phys. Rev. Research 2, 033351 (2020)] report a power-law decay of positional order in numerical simulations of hard disks confined within hard parallel walls, which they interpret as a Kosterlitz-Thouless (KT)-type caging-uncaging transition. The proposed existence of such a transition in a quasi-one-dimensional system, however, contradicts long-held physical expectations. To clarify if the proposed ordering persists in the thermodynamic limit, we introduce an exact transfer matrix approach to expeditiously generate configurations of very large subsystems that are typical of equilibrium thermodynamic (infinite-size) systems. The power-law decay of positional order is found to extend only over finite distances. We conclude that the numerical simulation results reported are associated with a crossover unrelated to KT-type physics, and not with a proper thermodynamic phase transition.

Enhancement of sound absorption in a band frequency using thin porous layer-lined metasurfaces

When a porous layer is installed on a hard wall, sound absorption performance is mainly determined by thickness of the layer. Although material parameters of porous materials are strongly dependent on frequencies, the thickness limitation related to the quarter wavelength of incident sound wave has been a key factor in the treatment of porous layers for noise reduction. This implies that a thicker porous layer is required to absorb lower-frequency sound effectively. To overcome the thickness limitation, metaporous layers, which are named as a compound of sound absorbing porous layers with the concept of metamaterials have received much attentions for alternative implementations of porous layers. Recently, we proposed a new type of metaporous layer for enhancing sound absorption performance in a specified broad frequency band. The proposed metaporous layer is constructed with a thin porous layer backed by a reactive metasurface consisting of an array of bent channels. Formation of sound absorption band is directly determined by the characteristics of scattered sound field from the proposed metaporous layer. Analytical and numerical investigations show that the metasurface is considerably responsible for the enhanced sound absorption in the proposed metaporous layer, while sound dissipation occurs only in the thin porous layer.

The effect of the convective momentum transfer on the acoustic boundary condition of perforated liners with grazing mean flow

The interaction of sound with sound-permeable hard walls subjected to grazing mean flow is investigated with a focus on the sound-induced exchange of streamwise momentum between the mean flow and the wall. Two generic wall types have to be distinguished, the homogeneously permeable wall and the wall with clearly separated openings, which is a more realistic model of technically feasible walls. To begin with, the focus is on the shear stress that drives the dynamics of the shearing mean flow over the homogeneous wall. This is analyzed by means of two simple mathematical models of shear stress diffusion, which come as two equivalent pairs of differential equations either for the acoustic shear stress and the wall-normal displacement, or for the streamwise and the wall-normal components of the acoustic velocity. The physical analysis is concentrated on the relation between shear stress and the wall-normal displacement of the fluid elements, which determines the effective admittance of the wall. The shear stress is represented by the momentum transfer impedance which is defined as the ratio between the acoustic wall shear stress and the in-wall velocity evaluated at the wall. It turns out that the strong increase of the acoustic wall shear stress due to transfer of mean flow momentum to the wall is the dominating mechanism which affects the effective admittance of the wall. Nevertheless, the suitability of the momentum transfer impedance as part of a complete boundary condition of the wall is questioned. The disagreement between the predicted momentum transfer impedance and some rare experimental data obtained with real inhomogeneous walls is considered as a strong indication that some further mechanisms are invoked by the inhomogeneity of real walls which are briefly discussed with regard to future studies.

Quantitative assessment of parallel acoustofluidic device.

The advantage of ultrasonic fields in harmless and label-free applications intrigued researchers to develop this technology. The capability of acoustofluidic technology for medical applications has not been thoroughly analyzed and visualized. Toward efficient design, in this research, flowing fluid in a microchannel excited by acoustic waves is fully investigated. To study the behavior of acoustic streaming, the main interfering parameters such as inlet velocity, working frequency, displacement amplitude, fluid buffer material, and hybrid effect in a rectangular water-filled microchannel actuated by standing surface acoustic waves are studied. Governing equations for acoustic field and laminar flow are derived employing perturbation theory. For each set of equations, appropriate boundary conditions are applied. Results demonstrate a parallel device is capable of increasing the inlet flow for rapid operations. Frequency increment raises the acoustic streaming velocity magnitude. Displacement amplitude amplification increases the acoustic streaming velocity and helps the streaming flow dominate over the incoming flow. The qualitative analysis of the hybrid effect shows using hard walls can significantly increase the streaming power without depleting excessive energy. A combination of several effective parameters provides an energy-efficient and fully controllable device for biomedical applications such as fluid mixing and cell lysis.

Confined Quantum Hard Spheres.

We present computer simulation and theoretical results for a system of N Quantum Hard Spheres (QHS) particles of diameter and mass m at temperature T, confined between parallel hard walls separated by a distance , within the range . Semiclassical Monte Carlo computer simulations were performed adapted to a confined space, considering effects in terms of the density of particles , where V is the accessible volume, the inverse length and the de Broglie’s thermal wavelength , where k and h are the Boltzmann’s and Planck’s constants, respectively. For the case of extreme and maximum confinement, and , respectively, analytical results can be given based on an extension for quantum systems of the Helmholtz free energies for the corresponding classical systems.

Coulomb corrections to two-particle interactions in artificial traps

In present work, we discuss the effect of Coulomb interaction to the dynamics of two-particle system bound in various traps. The strategy of including Coulomb interaction into the quantization condition of trapped system is discussed in a general and non-perturbative manner. In most cases, Coulomb corrections to quantization condition largely rely on numerical approach or perturbation expansion. Only for some special cases, such as the spherical hard wall trap, a closed-form of quantization condition with all orders of Coulomb corrections can be obtained.