Unique Boundary Research Articles

Lower Crustal Heterogeneity Beneath the Northern Tibetan Plateau Constrained by GPS Measurements Following the 2001 Mw7.8 Kokoxili Earthquake

AbstractWe use GPS measurements across the Xidatan segment of the Kunlun fault in the Tibetan Plateau to investigate the surface deformation following the 2001 Mw 7.8 Kokoxili earthquake. We find significant postseismic deformation during the period 2007–2015, characterized by an asymmetric shear across the 2001 rupture, with average velocities reaching ~10 mm/year about 30–45 km south of the coseismic rupture. We also find that the postseismic transients diffused away from the coseismic rupture through time, with a shift of the maximum transient rates from ~20–30 km south of the rupture in 2001–2002 to ~30–45 km in 2007–2015. Viscoelastic relaxation is the dominant physical process during the period 2007–2015. The estimated effective viscosity of the lower crust beneath the Songpan‐Ganzi terrane is 2 × 1018–3 × 1018 Pa s from the 2001–2002 data, and it has increased to ~2 × 1019 Pa s for the period 6 to 14 years after the event. The large asymmetry in the postseismic deformation field indicates a laterally heterogeneous lower crust beneath the northern Tibetan Plateau. Viscoelastic relaxation models show that the viscosity of the lower crust beneath the Qaidam basin is ~2 and ~4 times larger than the viscosity of the lower crust beneath the Songpan‐Ganzi terrane in 2001–2002 and 2007–2015, respectively. Based on these data and results from previous studies, we postulate that the Kunlun fault itself is not the unique rheological boundary and that additional domains with viscosity increasing from the Qiangtang terrane to the Qaidam basin appear to be required.

Classification of Urban Focal Points Based on Cluster Analysis

The article presents cluster analysis algorithms used to assess traffic demand and to define the urban territories (focal points (FPs)) as separate clusters (groups) allowing proving/disproving the necessity of territories (FPs) merging on the basis of stated indicators with mathematical precision. The relevance of developing the classification of urban FPs within the context of basic parameters of their functioning is defined. The uniqueness boundary of FP is determined which is used as the base of classifying FPs. The cluster analysis is discussed, namely, its advantages and disadvantages. The goal of the cluster analysis is stated as applied to traffic demand assessment. The cluster analysis is applied to each of 6 enlarged types of territories (FPs): warehousing and utilities; industry; offices; education, healthcare, sport, culture, leisure; trading, public catering, service sector; housing sector.

Topological insulator nanoribbons – A new paradigm for high thermoelectric performance

Thermoelectric (TE) materials, with the ability to convert heat directly to electricity, have attracted worldwide increasing attention due to the strong urge for clean energy today. However conventional TE devices suffer from the low conversion efficiency for decades due to the trade-off between TE parameters. Novel quantum materials such as topological insulators with unique boundary states protected topologically against backscattering offer a new way for designing high-performance TE devices. Here we demonstrate that topological insulator nanoribbons, which exhibit unconventional TE behaviors, can greatly improve the TE efficiency. As an example, we calculate the TE properties of the ZrTe5 nanoribbon through the Boltzmann transport theory with the electronic bands and the thermal conductivity obtained from ab initio calculations. The dramatic difference in the scattering intensity between the in-gap topological edge states and the bulk states originates several unusual TE behaviors: (I) The electrical to electronic thermal conductivity ratio can be several times larger than that predicted by the Wiedemann-Franz law. (II) The reduced Seebeck coefficient shows an anomalous opposite sign to that of normal semiconductors with the magnitude much larger than unity. (III) By properly introducing defects, the thermal conductivity can be significantly reduced without noticeably deteriorating the electrical conductivity. (IV) Under appropriate strain, the electrical to electronic thermal conductivity ratio could be tens of times larger due to the bulk gap narrowing. These results indicate that a figure of merit larger than ten is highly likely.

Evidence for allocentric boundary and goal direction information in the human entorhinal cortex and subiculum

In rodents, cells in the medial entorhinal cortex (EC) and subiculum code for the allocentric direction to environment boundaries, which is an important prerequisite for accurate positional coding. Although in humans boundary-related signals have been reported, there is no evidence that they contain allocentric direction information. Furthermore, it has not been possible to separate boundary versus goal direction signals in the EC/subiculum. Here, to address these questions, we had participants learn a virtual environment containing four unique boundaries. Participants then underwent fMRI scanning where they made judgements about the allocentric direction of a cue object. Using multivariate decoding, we found information regarding allocentric boundary direction in posterior EC and subiculum, whereas allocentric goal direction was decodable from anterior EC and subiculum. These data provide the first evidence of allocentric boundary coding in humans, and are consistent with recent conceptualisations of a division of labour within the EC.

Explosive solutions of elliptic equation with singular weight

Some instances of explosive solution to elliptic equation of the form in a bounded smooth domain have been studied but only the case b is constant or seem to have been considered up to now, at the best of our knowledge. In this paper, b is a positive weight function which can be singular on . We obtain existence, uniqueness and exact boundary behaviour of positive solution.

A Multibeam Interference Model for Analyzing Complex Near‐Field Images of Polaritons in 2D van der Waals Microstructures

AbstractVan der Waals (vdW) materials are among the most promising candidates for photonic integrated circuits because they support a full set of polaritons that can manipulate light at deep subdiffraction nanoscale. It is possible to directly probe the propagating polaritons in vdW materials in real space via scattering‐type scanning near‐field optical microscopy, such that the wave vector and lifetime of the polaritons can be extracted from as‐measured interference fringes by Fourier analysis. However, this method is unsuitable for clutter interference patterns in samples exhibiting inadequate fringes due to small size (less than 10 µm) or complex edges that are often encountered in nanophotonic devices and new material characterization. Here, a multibeam interference model is developed to analyze complex images by disentangling them into periodic patterns and residue. By employing phase stationary approximation, polariton wave vector can be derived from offset ratio of the center point, and the ratio of polariton reflection and scattering rates at the edge is obtained from the ratio of the periodic and aperiodic patterns. This method can be widely used in the optical characterization of new vdW materials that are difficult to synthesize into large crystals, as well as nanophotonic integrated devices with unique boundaries.

Purely rotational symmetry-protected topological crystalline insulator -Bi4Br4

Rotational-symmetry-protected topological crystalline insulators (TCIs) are expected to host unique boundary modes, in that the surface normal to the rotational axis can feature surface states with ‘unpinned’ Dirac points, which are not constrained to lie on high symmetry points or lines, but can lie at any general k point in the Brillouin zone. Also, as a higher order bulk boundary correspondence is involved here, a three-dimensional (3D) TCI can support one-dimensional (1D) helical edge states. Using first-principles band structure calculations, we identify the van der Waals material -Bi4Br4 as a purely rotation symmetry protected TCI. We show that the surface of Bi4Br4 exhibits a pair of unpinned topological Dirac fermions which are related to the presence of a two-fold rotation axis. These unpinned Dirac fermions possess an exotic spin texture which will be highly favorable for spin transport, and a band structure that consists of van Hove singularities due to a Lifshitz transition. We also identify 1D topological hinge states along the edges of an -Bi4Br4 rod. We comment on how the predicted topological features in -Bi4Br4 could be accessed experimentally.

Mechanical behaviour of a compacted well-graded granular material with and without cement

Cement additions improve the performance of granular soils. However, most literature examples of cement additions are in poorly graded sands, either to mimic the behaviour of sandstones or to accentuate the mechanical differences between cemented and uncemented soils. In this article, the behaviour of a well graded granular soil, used for base and sub-base of roads, was studied by doing triaxial tests on cemented and uncemented samples. Samples were compacted to achieve a dense fabric and tested at stresses commonly used in practice. Sieving was used to understand if breakage is important and to determine the grain size distributions of the samples after compaction and shearing. The results show that the addition of small percentages of cement greatly increase stiffness and dilation. Thereby, generating larger strengths; this is particularly important at low confining stresses in roads and parking areas, where this material is commonly used. At large strains, the results show that different Critical State Lines exist for both the uncemented and cemented soils. Each line has a different slope, which is believed to be the result of the evolution of the grain size distribution of the cemented soil. The normalised data indicate that a unique state boundary surface can be determined for all three tested soils.

Classification of 3+1D Bosonic Topological Orders (II): The Case When Some Pointlike Excitations Are Fermions

In this paper, we classify EF topological orders for 3+1D bosonic systems where some emergent pointlike excitations are fermions. (1) We argue that all 3+1D bosonic topological orders have gappable boundary. (2) All the pointlike excitations in EF topological orders are described by the representations of $G_f=Z_2^f\leftthreetimes_{e_2} G_b$ -- a $Z_2^f$ central extension of a finite group $G_b$ characterized by $e_2\in H^2(G_b,Z_2)$. (3) We find that the EF topological orders are classified by 2+1D anomalous topological orders $\mathcal{A}_b^3$ on their unique canonical boundary. Here $\mathcal{A}_b^3$ is a unitary fusion 2-category with simple objects labeled by $\hat G_b=Z_2^m\leftthreetimes G_b$. $\mathcal{A}_b^3$ also has one invertible fermionic 1-morphism for each object as well as quantum-dimension-$\sqrt 2$ 1-morphisms that connect two objects $g$ and $gm$, where $g\in \hat G_b$ and $m$ is the generator of $Z_2^m$. (4) When $\hat G_b$ is the trivial $Z_2^m$ extension, the EF topological orders are called EF1 topological orders, which is classified by simple data $(G_b,e_2,n_3,\nu_4)$. (5) When $\hat G_b$ is a non-trivial $Z_2^m$ extension, the EF topological orders are called EF2 topological orders, where some intersections of three stringlike excitations must carry Majorana zero modes. (6) Every EF2 topological order with $G_f=Z_2^f\leftthreetimes G_b$ can be associated with a EF1 topological order with $G_f=Z_2^f\leftthreetimes \hat G_b$. (7) We find that all EF topological orders correspond to gauged 3+1D fermionic symmetry protected topological (SPT) orders with a finite unitary symmetry group. (8) We further propose that the general classification of 3+1D topological orders with finite unitary symmetries for bosonic and fermionic systems can be obtained by gauging or partially gauging the finite symmetry group of 3+1D SPT phases of bosonic and fermionic systems.

Slices of parameter spaces of generalized Nevanlinna functions

In the early 1980's, computers made it possible to observe that in complex dynamics, one often sees dynamical behavior reflected in parameter space and vice versa. This duality was first exploited by Douady, Hubbard and their students in early work on rational maps.Here, we extend these ideas to transcendental functions.In [16], it was shown that for the tangent family, $ \{ \lambda \tan z \} $, the hyperbolic components meet at a parameter $ \lambda^* $ such that $ f_{ \lambda^*}^n( \lambda^*i) = \infty $ for some $ n $. The behavior there reflects the dynamic behavior of $ \lambda^* \tan z $ at infinity. In Part 1. we show that this duality extends to a more general class of transcendental meromorphic functions $ \{f_{\lambda}\} $ for which infinity is not an asymptotic value. In particular, we show that in 'dynamically natural' one-dimensional slices of parameter space, there are 'hyperbolic-like' components $ \Omega $ with a unique distinguished boundary point such that for $ \lambda \in \Omega $, the dynamics of $ f_\lambda $ reflect the behavior of $ f_\lambda $ at infinity. Our main result is that every parameter point $ \lambda $ in such a slice for which the iterate of the asymptotic value of $ f_\lambda $ is a pole is such a distinguished boundary point.In the second part of the paper, we apply this result to the families $ \lambda \tan^p z^q $, $ p, q \in \mathbb Z^+ $, to prove that all hyperbolic components of period greater than $ 1 $ are bounded.

Amorphous Intergranular Films Mitigate Radiation Damage in Nanocrystalline Cu-Zr

Nanocrystalline metals are promising radiation tolerant materials due to their large interfacial volume fraction, but irradiation-induced grain growth can eventually degrade any improvement in radiation tolerance. Therefore, methods to limit grain growth and simultaneously improve the radiation tolerance of nanocrystalline metals are needed. Amorphous intergranular films are unique grain boundary structures that are predicted to have improved sink efficiencies due to their increased thickness and amorphous structure, while also improving grain size stability. In this study, ball milled nanocrystalline Cu-Zr alloys are heat treated to either have only ordered grain boundaries or to contain amorphous intergranular films distributed within the grain boundary network, and are then subjected to in situ transmission electron microscopy irradiation and ex situ irradiation. Differences in defect density and grain growth due to grain boundary complexion type are then investigated. When amorphous intergranular films are incorporated within the material, fewer and smaller defect clusters are observed while grain growth is also limited, leading to nanocrystalline alloys with improved radiation tolerance.

Characterization of a Nanocrystalline Structure Formed by Crystal Lattice Transformation in a Bulk Steel Material

The formation of nanocrystalline structures in bulk metal materials is of great significance for both investigating the structural features of nanocrystalline materials and enhancing the value of bulk metal materials in engineering applications. Herein, we report a nanocrystalline structure formed by lattice transformation in a three-dimensional bulk metal material. We characterized its phase composition, three-dimensional features, and boundary structure. This nanocrystalline structure had microscale length and height and nanoscale width, which gave it a “nanoplate” structure in three-dimensional space. We observed edge dislocations in the interior of the nanocrystalline structure. A unique transitional boundary that contributed to maintaining its nanoscale size was found at the border between the parent phase and the nanocrystalline structure.

Second-order photonic topological insulator with corner states

Higher-order topological insulators (HOTIs) which go beyond the description of conventional bulk-boundary correspondence, broaden the understanding of topological insulating phases. Being mainly focused on electronic materials, HOTIs have not been found in photonic systems yet. In this article, we propose a type of two-dimensional second-order photonic crystals with zero-dimensional corner states and one-dimensional boundary states for optical frequencies. All of these states are topologically non-trivial and can be understood based on the theory of topological polarization. Moreover, by tuning the easily-fabricated structure of the photonic crystals, we can realize different topological phases with unique topological boundary states straightforwardly. Our result can be generalized to higher dimensions and provides unprecedented venues for higher-order photonic topological insulators and semimetals.

Photonics meets topology.

The topological phases in materials have been studied in recent decades for their unique boundary states and transport properties. Photonic systems with band structures embrace the topological phases closely, where they not only provide platforms to testify the topological band theory, but also shed light on designing novel optical devices. In this review, we present exciting developments, supported by brief descriptions of prominent milestones of topological phases in photonic systems in recent years. These studies may sustain further developments of optical devices and offer novel methods for light manipulations.

Lithofacies uncertainty modeling in a siliciclastic reservoir setting by incorporating geological contacts and seismic information

Deterministic modeling lonely provides a unique boundary layout, depending on the geological interpretation or interpolation from the hard available data. Changing the interpreter’s attitude or interpolation parameters leads to displacing the location of these borders. In contrary, probabilistic modeling of geological domains such as lithofacies is a critical aspect to providing information to take proper decision in the case of evaluation of oil reservoirs parameters, that is, applicable for quantification of uncertainty along the boundaries. These stochastic modeling manifests itself dramatically beyond this occasion. Conventional approaches of probabilistic modeling (object and pixel-based) mostly suffers from consideration of contact knowledge on the simulated domains. Plurigaussian simulation algorithm, in contrast, allows reproducing the complex transitions among the lithofacies domains and has found wide acceptance for modeling petroleum reservoirs. Stationary assumption for this framework has implications on the homogeneous characterization of the lithofacies. In this case, the proportion is assumed constant and the covariance function as a typical feature of spatial continuity depends only on the Euclidean distances between two points. But, whenever there exists a heterogeneity phenomenon in the region, this assumption does not urge model to generate the desired variability of the underlying proportion of facies over the domain. Geophysical attributes as a secondary variable in this place, plays an important role for generation of the realistic contact relationship between the simulated categories. In this paper, a hierarchical plurigaussian simulation approach is used to construct multiple realizations of lithofacies by incorporating the acoustic impedance as soft data through an oil reservoir in Iran.

Designing antiphase boundaries by atomic control of heterointerfaces

Extended defects are known to have critical influences in achieving desired material performance. However, the nature of extended defect generation is highly elusive due to the presence of multiple nucleation mechanisms with close energetics. A strategy to design extended defects in a simple and clean way is thus highly desirable to advance the understanding of their role, improve material quality, and serve as a unique playground to discover new phenomena. In this work, we report an approach to create planar extended defects-antiphase boundaries (APB) -with well-defined origins via the combination of advanced growth, atomic-resolved electron microscopy, first-principals calculations, and defect theory. In La2/3Sr1/3MnO3 thin film grown on Sr2RuO4 substrate, APBs in the film naturally nucleate at the step on the substrate/film interface. For a single step, the generated APBs tend to be nearly perpendicular to the interface and propragate toward the film surface. Interestingly, when two steps are close to each other, two corresponding APBs communicate and merge together, forming a unique triangle-shaped defect domain boundary. Such behavior has been ascribed, in general, to the minimization of the surface energy of the APB. Atomic-resolved electron microscopy shows that these APBs have an intriguing antipolar structure phase, thus having the potential as a general recipe to achieve ferroelectric-like domain walls for high-density nonvolatile memory.

A Novel Single-Terminal Fault Location Method for AC Transmission Lines in a MMC-HVDC-Based AC/DC Hybrid System

Accurate and reliable fault location method for alternating current (AC) transmission lines is essential to the fault recovery. MMC-based converter brings exclusive non-linear characteristics to AC networks under single-phase-to-ground faults, thus influencing the performance of the fault location method. Fault characteristics are related to the control strategies of the converter. However, the existing fault location methods do not take the control strategies into account, with further study being required to solve this problem. The influence of the control strategies to the fault compound sequence network is analyzed in this paper first. Then, a unique boundary condition that the fault voltage and negative-sequence fault current merely meet the direct proportion linear relationship at the fault point, is derived. Based on these, a unary linear regression analysis is performed, and the fault can be located according to the minimum residual sum function principle. The effectiveness of the proposed method is verified by PSCAD/EMTDC simulation platform. A large number of simulation results are used to verify the advantages on sampling frequency, fault resistance, and fault distance. More importantly, it provides a higher ranging precision and has extensive applicability.

Preparation of Photoluminescent Molybdenum Disulfide Quantum Dots for Biomedical Imaging

Since the discovery of graphene, great attention has been paid to transition metal disulfide two-dimensional layered materials due to their exceptional physical and chemical properties. Recently, molybdenum disulfide (MoS2) quantum dots (QDs) have been extensively investigated because of their unique quantum confinement and boundary effects as well as potential applications in fluorescence imaging, electrochemical catalysis, and biosensors. The preparation of MoS2 quantum dots can be divided into two types: bottom-up method and top-down method. In order to prepare aqueous MoS2 QDs solution, in this study, we develop a bottom-up strategy to synthesize MoS2 QDs using a simple, one-step hydrothermal method with ammonium tetrathiomolybdate [(NH4)2MoS4] as the precursor and hydrazine hydrate as the reducing agent. The morphology and structural characteristics of MoS2 QDs are analyzed by transmission electron microscopy, and optical properties are characterized using UV-Vis and photoluminescence spectroscopy. Also, the cytotoxicity of MoS2 QDs are tested. Experimental results demonstrate that MoS2 QDs can be used for biomedical imaging and drug delivery carriers.

Preparation of Photoluminescent Molybdenum Disulfide Quantum Dots for Biomedical Imaging

Recently, molybdenum disulfide (MoS2) quantum dots (QDs) have been extensively investigated because of their unique quantum confinement and boundary effects as well as potential applications in fluorescence imaging, electrochemical catalysis, and biosensors. In this study, we synthesize MoS2 QDs by using a one-step hydrothermal method with ammonium tetrathiomolybdate as the precursor and hydrazine hydrate as the reducing agent. The morphology and structural characteristics of MoS2 QDs are analyzed by transmission electron microscopy, and optical properties are characterized using UV-Vis absorption and photoluminescence spectroscopy. The cytotoxicity of MoS2 QDs is tested by MTT assay. MoS2 QDs in biomedical imaging is demonstrated by a simple incubation study with U251 cells. Experimental results demonstrate that MoS2 QDs can be used for biomedical imaging applications.

Ascertaining when a basin is Wada: the merging method

Trying to imagine three regions separated by a unique boundary seems a difficult task. However, this is exactly what happens in many dynamical systems showing Wada basins. Here, we present a new perspective on the Wada property: A Wada boundary is the only one that remains unaltered under the action of merging the basins. This observation allows to develop a new method to test the Wada property, which is much faster than the previous ones. Furthermore, another major advantage of the merging method is that a detailed knowledge of the dynamical system is not required.