Anisotropic Geometry Research Articles

Assembling anisotropic colloids using curvature-mediated lipid sorting.

The use of colloid supported lipid bilayers (CSLBs) for assembling colloidal structures has been of recent interest. Here, we use multi-component lipid bilayer membranes formed around anisotropic colloids and show that the curvature anisotropy of the colloids drives a sorting of the lipids in the membrane along the colloids. We then exploit this curvature-sensitive lipid sorting to create "shape-anisotropic patchy colloids" - specifically, we use colloids with six rods sticking out of a central cubic core, "hexapods", for this purpose and demonstrate that membrane patches self-assemble at the tip of each of the six colloidal rods. The membrane patches are rendered sticky using biotinylated lipids in complement with a biotin-binding streptavidin protein. Finally, using these "shape-anisotropic patchy colloids", we demonstrate the directed assembly of colloidal links, paving the way for the creation of heterogeneous and flexible colloidal structures.

Isotropization of locally rotationally symmetric Bianchi-I universe in f(Q)-gravity

Despite having the somewhat successful description of accelerated cosmology, the early evolution of the universe always challenges mankind. Our promising approach lies in a new class of symmetric teleparallel theory of gravity named f(Q), where the non-metricity scalar Q is responsible for the gravitational interaction, which may resolve some of the issues. To study the early evolution of the universe, we presume an anisotropic locally rotationally symmetric (LRS) Bianchi-I spacetime and derive the motion equations. We discuss the profiles of energy density, equation of state and skewness parameter and observe that our models archive anisotropic spatial geometry in the early phase of the universe with a possible presence of anisotropic fluid and as time goes on, even in the presence of an anisotropic fluid, the universe could approach isotropy due to inflation and the anisotropy of the fluid fades away at the same time.

Learning Discriminative Features by Covering Local Geometric Space for Point Cloud Analysis

At present, effectively aggregating and transferring the local features of point cloud is still an unresolved technological conundrum. In this study, we propose a new space-cover convolutional neural network (SC-CNN) for tasks such as point cloud classification and segmentation. The core of this network is space-cover convolution (SC-Conv), which implements depthwise separable convolution on the point cloud. In addition, a newly designed space-cover operator (SCOP) replaces depthwise convolution. The key to SC-Conv is constructing anisotropic spatial geometry in the local point cloud. The SCOP achieves this by utilizing the positional and feature relationships to learn the high-order relationship expression between points. First, data-driven adaptive learning from the 3-D coordinate relationship between the local points is used to determine the weight of the SCOP. Then, the edge feature of the neighboring point relative to the sampling point is used as the input of the SCOP. Finally, a deformable spatial geometry is constructed in the feature space between local points to aggregate the local high-order features. By stacking SC-Conv to construct SC-CNN with a hierarchical network structure for point cloud analysis, we can better perceive the shape information of point cloud and improve network robustness. Finally, we provide numerous experiments to verify that SC-CNN parallels or even outperforms advanced methods in shape classification, part segmentation, and large-scale indoor scene segmentation tasks. The open-source code was published at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/changshuowang/SC-CNN</uri> .

Interfacial Stress‐Modulated Mechanosensitive Upconversion Luminescence of NaErF4 Based Heteroepitaxial Core–Shell Nanoparticles

AbstractThe resulting interfacial stress in heteroepitaxial nanocomplex usually has negligible influence on its performance, but at high pressures (HP) the effect can be significantly amplified. In order to unravel the underlying mechanism and search for high quality pressure sensors, a simple object is employed, NaErF4@NaLnF4 (Ln = Y, Lu, Gd) and its Tm3+‐doped derivatives, to comparatively study the effect of interfacial stress on upconversion (UC) luminescence. Specifically, the doping enhances greatly mechanosensitivity because of the anisotropic local geometry of the dopant ions of which the structural distortion is amplified by HP. The generated compressive strain does extend into the core as witnessed by the effect of tensile strain in the shell on the core and the fact that Lu‐shelled nanoparticles are the most sensitive to external force among Tm3+‐doped system. This compressive strain in concert with the external HP intensifies the coupling between Er3+ and Tm3+, making the attenuation of green UC emission more pronounced. The red to green UC emission ratio of this material, robust both in structural and optical properties, increases linearly with pressure in the range from ambient to 9 GPa. The study opens a new horizon for understanding the effect of interfacial stress on UC luminescence.

A new way to test the Cosmological Principle: measuring our peculiar velocity and the large-scale anisotropy independently

We present a novel approach to disentangle two key contributions to the largest-scale anisotropy of the galaxy distribution: (i) the intrinsic dipole due to clustering and anisotropic geometry, and (ii) the kinematic dipole due to our peculiar velocity. Including the redshift and angular size of galaxies, in addition to their fluxes and positions allows us to measure both the direction and amplitude of our velocity independently of the intrinsic dipole of the source distribution.We find that this new approach applied to future galaxy surveys (LSST and Euclid) and a SKA radio continuum survey will allow to measure our velocity (β = v/c) with a relative error in the amplitude σ(β)/β ∼ (1.3–4.5)% and in direction, θβ ∼ 0.9°–3.9°, well beyond what can be achievedwhen analysing only the number count dipole.We also find that galaxy surveys are able to measure the intrinsic large-scale anisotropy with a relative uncertainty of ≲5% (measurement error, not including cosmic variance).Our method enables two simultaneous tests of the Cosmological Principle: comparing the observations of our peculiar velocity with the CMB dipole, and testing for a significant intrinsic anisotropy on large scales which would indicate effects beyond the standard cosmological model.

Aligned natural inflation in the Large Volume Scenario

We embed natural inflation in an explict string theory model and derive observables in cosmology. We achieve this by compactifying the type IIB string on a Calabi-Yau orientifold, stabilizing moduli via the Large Volume Scenario, and configuring axions using D7-brane stacks. In order to obtain a large effective decay constant, we employ the Kim-Nilles-Peloso alignment mechanism, with the required multiple axions arising naturally from generically anisotropic bulk geometries. The bulk volumes, and hence the axion decay constants, are stabilized by generalized one-loop corrections and subject to various conditions: the Kähler cone condition on the string geometry; the convex hull condition of the weak gravity conjecture; and the constraint from the power spectrum of scalar perturbations. We find that all constraints can be satisfied in a geometry with relatively small volume and thus heavy bulk axion mass. We also covariantize the convex hull condition for the axion-dilaton-instanton system and verify the normalization of the extremal bound.

Hyperbolic Metamaterials Fabricated Using 3D Assembled Nanorod Arrays and Enhanced Photocatalytic Performance

AbstractIt is significant but challenging to develop a 3D colloidal assembly method for optical metamaterials. Hyperbolic metamaterials (HMMs) with 3D porous periodic morphologies are suitable for loading functional components for energy harvesting and biosensing and for providing a tunable range of indefinite permittivity. In this study, porous HMMs with 3D periodicities are constructed from directionally assembled silica nanorods with conformal coating of metal. The indefinite dielectric ranges around visible wavelength are formed from the anisotropic geometry induced anisotropic effective permittivity along different directions and are tunable according to the rod length, rod diameter, and thickness of metal coating. The negative refraction of rod array based metamaterials is verified using the transmission ratio between the part beam and full beam in microscope–spectrum system with incident light beam. The rod‐based metamaterials show a higher optical absorption in near‐ultraviolet and visible wavelengths than the compared colloidal sphere assembled structures. The porous HMMs loaded with TiO2 can provide enhanced optical absorption and photocatalytic performances. The structures coated with 180–190 atomic‐layer‐deposition cycles of TiO2 and 8–9 min deposition of silver provide the best performance.

Sensitivity of SK(K)S and ScS phases to heterogeneous anisotropy in the lowermost mantle from global wavefield simulations

SUMMARY Observations of seismic anisotropy at the base of the mantle are abundant. Given recent progress in understanding how deformation relates to anisotropy in lowermost mantle minerals at the relevant pressure and temperature conditions, these observations can be used to test specific geodynamic scenarios, and have the potential to reveal patterns of flow at the base of the mantle. For example, several recent studies have sought to reproduce measurements of shear wave splitting due to D″ anisotropy using models that invoke specific flow and texture development geometries. A major limitation in such studies, however, is that the forward modelling is nearly always carried out using a ray theoretical framework, and finite-frequency wave propagation effects are not considered. Here we present a series of numerical wave propagation simulation experiments that explore the finite-frequency sensitivity of SKS, SKKS and ScS phases to laterally varying anisotropy at the base of the mantle. We build on previous work that developed forward modelling capabilities for anisotropic lowermost mantle models using the AxiSEM3D spectral element solver, which can handle arbitrary anisotropic geometries. This approach enables us to compute seismograms for relatively short periods (∼4 s) for models that include fully 3-D anisotropy at moderate computational cost. We generate synthetic waveforms for a suite of anisotropic models with increasing complexity. We first test a variety of candidate elastic tensors in laterally homogeneous models to understand how different lowermost mantle elasticity scenarios express themselves in shear wave splitting measurements. We then consider a series of laterally heterogeneous models of increasing complexity, exploring how splitting behaviour varies across the edges of anisotropic blocks and investigating the minimum sizes of anisotropic heterogeneities that can be reliably detected using SKS, SKKS and ScS splitting. Finally, we apply our modelling strategy to a previously published observational study of anisotropy at the base of the mantle beneath Iceland. Our results show that while ray theory is often a suitable approximation for predicting splitting, particularly for SK(K)S phases, full-wave effects on splitting due to lowermost mantle anisotropy can be considerable in some circumstances. Our simulations illuminate some of the challenges inherent in reliably detecting deep mantle anisotropy using body wave phases, and point to new strategies for interpreting SKS, SKKS and ScS waveforms that take full advantage of newly available computational techniques in seismology.

Mathematical analysis of plasmon resonances for curved nanorods

We investigate plasmon resonances for curved nanorods which present anisotropic geometries. We analyze quantitative properties of the plasmon resonance and its relationship to the metamaterial configurations and the anisotropic geometries of the nanorods. Based on delicate and subtle asymptotic and spectral analysis of the layer potential operators, particularly the Neumann-Poincaré operators, associated with anisotropic geometries, we derive sharp asymptotic formulae of the corresponding scattering field in the quasi-static regime. By carefully analyzing the asymptotic formulae, we establish sharp conditions that can ensure the occurrence of the plasmonic resonance. The resonance conditions couple the metamaterial parameters, the wave frequency and the nanorod geometry in an intricate but elegant manner. We provide thorough resonance analysis by studying the wave fields both inside and outside the nanorod. Furthermore, our quantitative analysis indicates that different parts of the nanorod induce varying degrees of resonance. Specifically, the resonant strength at the two end-parts of the curved nanorod is more outstanding than that of the facade-part of the nanorod.

Manipulation of the Optical Properties of Colloidal 2D CdSe Nanoplatelets

Driven by the unique optoelectronic features arising from the strong quantum confinement along the thickness direction, rapid development of CdSe‐based nanoplatelets (NPL) has accomplished facile bandgap tunability over a broad spectrum via different preparation protocols or various postsynthesis treatments. The anisotropic geometry of NPLs also stimulates the exploitation of self‐assembled CdSe NPL superstructures to enhance light extraction efficiency in display technologies and achieves polarized lasing performance or even electrically pumped laser by adjusting the transition dipole orientation. Although several review articles about the general optical properties of CdSe NPLs have been published, none of them focus on the ability of spectral tunability and precise control of orientations in the solid‐state phase of CdSe NPLs. Herein, the band structure engineering approaches in the CdSe NPL family are systematically summarized and the optical properties and device performance metrics of these deliberately engineered NPLs are compared. Then, the recent advanced studies of the motivation and assembly methods of geometrically anisotropic CdSe NPL superlattices are discussed. Finally, the current challenges and future outlook on the controlled modification of optical features and the influences of the approaches in the aspect of CdSe NPL–based devices’ performance are highlighted.

Single‐Handed Double Helix and Spiral Platelet Formed by Racemate of Dissymmetric Cages

AbstractSpontaneous deracemization has been used to separate homochiral domains from the racemic system. However, homochirality can only be referred to when the scales of these domains and systems are specified. To clarify this, we report self‐assembly of racemates of dissymmetric cages DC‐1 with a cone‐shape propeller geometry, forming a centrosymmetric columnar crystalline phase (racemic at crystallographic level). Owing to their anisotropic geometry, the two enantiomers are packed in a frustrated fashion in this crystalline phase; single‐handed double helices are observed (single‐handedness at supramolecular level). The frustrated packing (layer continuity break‐up) in turn facilitates screw dislocation during the crystal growth, forming left‐ or right‐handed spiral platelets (symmetry‐breaking at morphological level), although each platelet is composed of DC‐1 racemates. The symmetry correlation between DC‐1 molecules, the crystalline phase and spiral platelets, all exhibit C3 symmetry.

Single-Handed Double Helix and Spiral Platelet Formed by Racemate of Dissymmetric Cages.

Spontaneous deracemization has been used to separate homochiral domains from the racemic system. However, homochirality can only be referred to when the scales of these domains and systems are specified. To clarify this, we report self-assembly of racemates of dissymmetric cages DC-1 with a cone-shape propeller geometry, forming a centrosymmetric columnar crystalline phase (racemic at crystallographic level). Owing to their anisotropic geometry, the two enantiomers are packed in a frustrated fashion in this crystalline phase; single-handed double helices are observed (single-handedness at supramolecular level). The frustrated packing (layer continuity break-up) in turn facilitates screw dislocation during the crystal growth, forming left- or right-handed spiral platelets (symmetry-breaking at morphological level), although each platelet is composed of DC-1 racemates. The symmetry correlation between DC-1 molecules, the crystalline phase and spiral platelets, all exhibit C3 symmetry.

AT2017gfo: Bayesian inference and model selection of multicomponent kilonovae and constraints on the neutron star equation of state

ABSTRACTThe joint detection of the gravitational wave GW170817, of the short γ-ray burst GRB170817A and of the kilonova AT2017gfo, generated by the the binary neutron star (NS) merger observed on 2017 August 17, is a milestone in multimessenger astronomy and provides new constraints on the NS equation of state. We perform Bayesian inference and model selection on AT2017gfo using semi-analytical, multicomponents models that also account for non-spherical ejecta. Observational data favour anisotropic geometries to spherically symmetric profiles, with a log-Bayes’ factor of ∼104, and favour multicomponent models against single-component ones. The best-fitting model is an anisotropic three-component composed of dynamical ejecta plus neutrino and viscous winds. Using the dynamical ejecta parameters inferred from the best-fitting model and numerical–relativity relations connecting the ejecta properties to the binary properties, we constrain the binary mass ratio to q &amp;lt; 1.54 and the reduced tidal parameter to $120\lt \tilde{\Lambda }\lt 1110$. Finally, we combine the predictions from AT2017gfo with those from GW170817, constraining the radius of a NS of 1.4 M⊙ to 12.2 ± 0.5 km (1σ level). This prediction could be further strengthened by improving kilonova models with numerical-relativity information.

Geometry and mineral heterogeneity controls on precipitation in fractures: An X-ray micro-tomography and reactive transport modeling study

The processes that affect reorganization of flow and transport in fractures during precipitation were investigated experimentally and numerically in order to highlight the interplay between calcite precipitation, flow and growth substrate. Calcite was precipitated from a supersaturated solution at two different flow rates (0.4 or 12 cm3·hr−1) into artificial fractures made in dolomitic limestone. Although the inlet fluid composition and temperature were identical for all the experiments, facture sealing and precipitation patterns were closely linked to the mineral substrate, fracture geometry and flow field reorganization. Calcite precipitation rate is highly variable along and between the flow paths and depends on the local saturation index of the reactive fluid. In addition, calcite precipitates preferentially on calcite comparatively to dolomite substrate. 2D reactive transport modeling accounting for the negative feedback between porosity and permeability decrease succeeded in quantitatively reproducing the experimental observations, such as the evolution of the fracture void obtained from X-ray micro-tomography (XMT), the evolution of the calcium breakthrough concentration and fracture sealing. The corresponding model was then used to evaluate the impacts of fluid flow and reactivity on randomly generated anisotropic fractures geometries. Simulation results reveal that the sealing capacity of fractures and associated reorganization of flow depends on the Damköhler number, i.e., the ratio between characteristic times for advective transport and reaction, although other factors like the fracture geometry and kinetic law play also a role at this stage. More importantly, the existence of a critical saturation index for initiating precipitation onto mineral substrate can substantially impair the prediction of the sealing capacity, and will depend on the spatial heterogeneity and connectivity of the mineral substrate. Most cases result in a strong precipitation gradient along the flow direction that will increase the permeability anisotropy. However, under certain conditions, precipitation allows the fracture to recover more isotropic properties that will lead back to a more uniform flow field and sealing. Negative feedback between precipitation process and transport during fracture closure supports a strong reorganization of flow of supersaturated fluids during geo-engineering operations.

Scattering by lossy anisotropic scatterers: A modal approach

Scattering from anisotropic geometries of arbitrary shape is relatively difficult to interpret physically, involving the intricate interplay between material and geometric effects. Insights into complex scattering mechanisms are often enabled by modal methods that decompose the response into the well-understood multipolar resonances. Here, we extend the generalized normal mode expansion to lossy and anisotropic scatterers. Unique to the method is that it decomposes the total response of any anisotropic resonator into the modes of the corresponding isotropic resonator. This disentangles the material and geometric contributions to the scattering of any anisotropic resonator. Furthermore, the method can identify absorption and scattering resonances with separate sets of modes. We illustrate our method by considering an infinitely long cylinder with concentric metallic/dielectric layers, targeting the complex case of an effective hyperbolic response. We show that by scanning the material composition of the hyperbolic medium, we can achieve any desired scattering effect, including backscattering cancellation.

Progress in rod bundle CHF in the past 40 years

Critical Heat Flux (CHF) prediction remains one of the most important tasks in thermal hydraulics of Light Water Reactors (LWR’s). During recent years, tremendous progress has been made in understanding and predicting rod bundle CHF. However, due to the unique features associated with rod bundle subchannel systems, including complex and compact anisotropic geometry, non-uniform axial/radial heating, open channel interactions, periodic (positional) mixing vane grids (MVG’s) mixing (Yang et al., 2014), and a broad range of operation conditions (Yang and Han et al., 2019), a precise prediction of CHF in rod bundles, entirely based on analytical methods without the support of any extensive experimental database, is still beyond the present modelling and computational capabilities. For Pressurized Water Reactors (PWR’s), CHF occurs at a relatively low coolant quality and is primarily driven by the Departure from Nucleate Boiling (DNB) type event, which can be triggered by liquid sublayer dryout, bubble crowding, homogeneous nucleation, or other mechanisms causing local starvation of liquid under subcooled flow boiling or low quality saturated boiling conditions, and the dryout event, which describes CHF under a high void situation when liquid film on the fuel surface dries out, usually happens in a high quality saturated annular flow. Boiling Water Reactors (BWR’s) operate at a relatively lower pressure and can reach much higher coolant qualities that correspond to annular two-phase flow conditions. This dominant CHF mechanism, dryout, is based on the gradual thinning and drying out of the liquid film.This paper provides an overview of the progress made in the experimental and analytical investigations of CHF in both PWR and BWR rod bundles during the past 40 years. A complete comprehensive concept map is developed to outline most of the key mechanistic CHF models covering the entire range of flow regimes. The limitation and the potential approaches for the application of mechanistic models to rod bundle CHF prediction are reviewed. This includes the recently proposed, rod bundle specific NHNM (Non-uniform heater Homogeneous Nucleation Model [Yang, 2017]). Various industrial empirical correlations are reviewed together with their corresponding subchannel codes and required rod bundle CHF experiments. The need for clear guidelines and standards for benchmarking new rod bundle CHF test facilities is discussed.Various approaches on investigating, understanding, modeling, and predicting the occurrence of rod bundle CHF are reviewed from mechanistic models, semi-empirical and empirical approaches to advanced CFD simulation. The achievements and limitations in those methods are discussed with suggestions for future advancement.

A comment: a set square design metamaterial absorber for X-band applications

Recently, Barde C, Choubey A, Sinha R. [A set square design metamaterial absorber for X-band applications. J Electromagn Waves Appl. 2020;34:1430–1443.] have demonstrated the metamaterial absorber for X-band applications. In the present communication, we numerically investigated that a cross-polarizer is mistakenly reported as a wideband metamaterial absorber. Authors ignored the cross-polarized reflection component in the calculation of the absorption. Moreover, it is proved that the anisotropic geometry of the unit cell provides poor absorption and it is suitable for the polarization conversion.

Statistical Piezotronic Effect in Nanocrystal Bulk by Anisotropic Geometry Control

AbstractUtilizing inner‐crystal piezoelectric polarization charges to control carrier transport across a metal‐semiconductor or semiconductor–semiconductor interface, piezotronic effect has great potential applications in smart micro/nano‐electromechanical system (MEMS/NEMS), human‐machine interfacing, and nanorobotics. However, current research on piezotronics has mainly focused on systems with only one or rather limited interfaces. Here, the statistical piezotronic effect is reported in ZnO bulk composited of nanoplatelets, of which the strain/stress‐induced piezo‐potential at the crystals’ interfaces can effectively gate the electrical transport of ZnO bulk. It is a statistical phenomenon of piezotronic modification of large numbers of interfaces, and the crystal orientation of inner ZnO nanoplatelets strongly influence the transport property of ZnO bulk. With optimum preferred orientation of ZnO nanoplatelets, the bulk exhibits an increased conductivity with decreasing stress at a high pressure range of 200–400 MPa, which has not been observed previously in bulk. A maximum sensitivity of 1.149 µS m−1 MPa−1 and a corresponding gauge factor of 467–589 have been achieved. As a statistical phenomenon of many piezotronic interfaces modulation, the proposed statistical piezotronic effect extends the connotation of piezotronics and promotes its practical applications in intelligent sensing.

Multifractal Alterations in Oral Sub-Epithelial Connective Tissue During Progression of Pre-Cancer and Cancer.

Bright-field microscopy (BFM) encrypts the optical transillumination profile of the transmitted light attenuated by the complex micro-structural tissue convolutions, manifested by the dense and compact regions of the specimen under examination. The connotations of idiosyncratic tissue interaction dynamics with the onset of pre-cancerous activity are encoded in the BFM acquired oral mucosa histopathological images (OMHI). In the present study, our analysis is focused on the sub-epithelium region of the oral mucosa, which has high clinical significance but sparsely explored in the literature from the textural domain. Histopathology being the gold-standard technique till date, we have used the light microscopic histopathology images for tissue characterization. The tissue-index transmission patches (TITP) from the sub-epithelium region are cropped under the guidance of oral onco-pathologists. After that, the TITPs are characterized for its multi-scale spatial-deformation dynamics, while keeping the intrinsic anisotropic geometry, and local contour connectivity within tolerable limits. With recent studies exhibiting multifractal's potency in diverse biological system analysis, here, we exploit the 2D multifractal detrended fluctuation analysis (2D-MFDFA) on TITPs for exploring a discriminative set of multifractal signatures for healthy, oral potentially malignant disorders and oral cancer tissue sample. The predictive model's competency is validated on an experimentally collected corpus of TITP samples and substantiated via confirmatory data statistics and analysis, showing its inter-class segregation efficacy. Moreover, the 2D-MFDFA analysis evinces the complex multifractal patterns in TITPs, which is due to the presence of composite long-range correlations in the oral mucosa tissue fabric.

Sharp estimate of electric field from a conductive rod and application

AbstractWe are concerned with the quantitative study of the electric field perturbation due to the presence of an inhomogeneous conductive rod embedded in a homogenous conductivity. We sharply quantify the dependence of the perturbed electric field on the geometry of the conductive rod. In particular, we accurately characterize the localization of the gradient field (i.e., the electric current) near the boundary of the rod where the curvature is sufficiently large. We develop layer‐potential techniques in deriving the quantitative estimates and the major difficulty comes from the anisotropic geometry of the rod. The result complements and sharpens several existing studies in the literature. It also generates an interesting application in EIT (electrical impedance tomography) in determining the conductive rod by a single measurement, which is also known as the Calderón's inverse inclusion problem in the literature.