Coherent Clusters Research Articles

Symmetry-specific orientational order parameters for complex structures.

A comprehensive framework of characterizing complex self-assembled structures with a set of orientational order parameters is presented. It is especially relevant in the context of using anisotropic building blocks with various symmetries. Two classes of tensor order parameters are associated with polyhedral nematic and bond orientational order. For the latter, a variation of classical bond order parameters (BOPs) is introduced, which takes advantage of the symmetry of constituent particles and/or expected crystalline phases. These symmetrized BOPs can be averaged over an entire system or assigned locally to an individual bond. By combining that with the bond percolation procedure, one is able to identify coherent domains within a self-assembled structure. As a demonstration of the proposed framework, we apply it to a simulated hybrid system that combines isotropic and patchy particles with octahedral symmetry. Not only does the methodology allow one to identify individual crystalline domains but also it detects coherent clusters of a peculiar compact amorphous structure that is not space-filling and lacks any long-range order.

Extreme shear deformation enables ultra-fast riveting of high strength aluminum alloys

Dispersed nano-precipitates strengthen high-strength aluminum (Al) alloys but reduce ductility and formability. Joining these alloys with conventional impact (or driven) riveting has long been a challenge because the rivets may crack in ambient conditions. Rotating hammer riveting (RHR) was developed to rivet fully hardened high-strength Al alloys 2024-T351 and 7075-T6. RHR eliminates the need to soften 7075 rivets by preheating or to store 2024 rivets at low temperature to preserve the annealed condition. Avoiding cracked rivet heads and shanks during RHR is attributed to high-strain-rate plastic deformation, which promotes dynamic recrystallization of grains and amorphization of second phases; this mitigates stress concentration and prevents microvoids. Meanwhile, the coherent solute atom clusters in the Al matrix are sheared by dislocation movement, not coarsened, because the thermal cycle is short (10−1 s). RHR obviates time- and cost-intensive prior and post-processing heat treatments, achieving high integrity between riveted and assembled components.

Subject specialties as interdisciplinary trading grounds: the case of the social sciences and humanities

In this study we explore the disciplinary diversity present within subject specialties in the social sciences and humanities. Subject specialties are operationalized as textually coherent clusters of documents. We apply topic modelling to textual information on the individual document level (titles and abstracts) to cluster a multilingual set of roughly 45,000 documents into subject specialties. The dataset includes the metadata of journal articles, conference proceedings, book chapters, and monographs. We make use of two indicators, namely, the organizational affiliation based on the departmental address of the authors and the cognitive orientation based on the disciplinary classifications at the publication level. First, we study the disciplinary diversity of the clusters by calculating a Hill-type diversity index. We draw an overall picture of the distribution of subject specialties over diversity scores and contrast the two indicators with each other. The goal is to discover whether some subject specialties are inherently multi- or interdisciplinary in nature, and whether the different indicators are telling a well-aligned, similar story. Second, for each cluster of documents we calculate the dominance, i.e. the relative size of the largest discipline. This proxy of disciplinary concentration gives an idea of the extent to which a specialty is disciplined. The results show that all subject specialties analyzed serve as interdisciplinary trading grounds, with outliers in both directions of the disciplinary-interdisciplinary continuum. For a large share of specialties, the dominant cognitive and organizational disciplinary classification were found to be well aligned. We present a typology of subject specialties by contrasting the organizational and cognitive diversity scores.

Controlling morphology in hybrid isotropic/patchy particle assemblies.

Brownian dynamics is used to study self-assembly in a hybrid system of isotropic particles (IPs), combined with anisotropic building blocks that represent special "designer particles." Those are modeled as spherical patchy particles (PPs) with binding only allowed between their patches and IPs. In this study, two types of PPs are considered: Octahedral PPs (Oh-PPs) and Square PPs (Sq-PPs), with octahedral and square arrangements of patches, respectively. The self-assembly is additionally facilitated by the simulated annealing procedure. The resultant structures are characterized by a combination of local correlations in cubatic ordering and a symmetry-specific variation of bond orientation order parameters (SymBOPs). By varying the PP/IP size ratio, we detected a sharp crossover between two distinct morphologies in both types of systems. High symmetry phases, NaCl crystal for Oh-PP and square lattice for Sq-PP, are observed for larger size ratios. For the smaller ones, the dominant morphologies are significantly different, e.g., Oh-PPs form a compact amorphous structure with predominantly face-to-face orientation of neighboring PPs. Unusually, for a morphology without a long-range order, it is still possible to identify well organized coherent clusters of this structure, thanks to the adoption of our SymBOP-based characterization.

In search of healthcare system ideal types — Changeable classifications and dimensions

This article aims to classify the healthcare systems of 43 developed economies into different healthcare system types, and to examine whether the dimensions of health system characteristics produce coherent health system classification when the dimensions are observed separately. We group health systems into different types based on their institutional structures and performance using healthcare financing, healthcare provision and health outcomes as dimensions of the health system characteristics. Unlike previous classifications, we classify each dimension separately using hierarchical cluster analysis. In particular dimensions, our results resemble those found in previous classifications. However, no coherent clustering of healthcare systems was found across the three dimensions. The results show that healthcare system dimensions differ from each other and each of them form their unique system types. Separating the dimensions helps detecting connections between the healthcare system types and phenomena being studied. It is relevant to note the differences of health system dimensions while discussing healthcare system classifications.

Impossibility to produce arbitrary non-Gaussian states using zero-mean Gaussian states and partial photon number resolving detection

Gaussian states and measurements collectively are not powerful-enough resources for quantum computing, as any Gaussian dynamics can be simulated efficiently, classically. However, it is known that any one non-Gaussian resource -- either a state, a unitary operation, or a measurement -- together with Gaussian unitaries, makes for universal quantum resources. Photon number resolving (PNR) detection, a readily-realizable non-Gaussian measurement, has been a popular tool to try and engineer non-Gaussian states for universal quantum processing. In this paper, we consider PNR detection of a subset of the modes of a zero-mean pure multi-mode Gaussian state as a means to herald a target non-Gaussian state on the undetected modes. This is motivated from the ease of scalable preparation of Gaussian states that have zero mean, using squeezed vacuum and passive linear optics. We calculate upper bounds on the fidelity between the actual heralded state and the target state. We find that this fidelity upper bound is $1/2$ when the target state is a multi-mode coherent cat-basis cluster state, a resource sufficient for universal quantum computing. This proves that there exist non-Gaussian states that are not producible by this method. Our fidelity upper bound is a simple expression that depends only on the target state represented in the photon-number basis, which could be applied to other non-Gaussian states of interest.

Harmonic vibration analysis with coherent‐nodal‐cluster two‐stage model reduction

AbstractLinear finite element harmonic vibration analysis is an important tool when investigating structural performance. In order to construct the requested frequency response functions by sweeping through the frequencies, the full finite element model is typically reduced by a Galerkin projection, using either the solution of a free vibration problem, or with load‐dependent Ritz vectors. Here we construct an approximation of the model reduction matrix using an intermediate reduced‐model stage based on the Coherent Nodal Clusters technique. Thus we arrive at a two‐stage model‐reduction procedure. Although there is an additional approximation the reduced models are obtained at a much lower cost than the one‐stage models. In order to ameliorate the loss of accuracy involved in the additional approximation, we introduce enhancement of the reduced bases by inexpensive residual‐minimizing iterations.

The petrified pedagogy of speech delivery: reexamining the Canon of speech delivery through the lens of nonverbal communication research

ABSTRACT Speech delivery pedagogy has both changed dramatically over the last several centuries and remained remarkably fixed over the last 100 years. In the early 1900s, this pedagogy underwent a dramatic shift from an “elocutionist approach” to a “natural approach” to speech delivery. Since that time, speech delivery pedagogy has remained in an essentially petrified state while our understanding of nonverbal behaviors – the very behaviors at the heart of speech delivery – has grown exponentially. In this essay, we draw upon the expansive nonverbal communication literature to argue for a new approach to teaching speech delivery – an approach we refer to as the interconnected approach. This interconnected approach re-emphasizes the importance of speech delivery, structures the topic of speech delivery around coherent nonverbal clusters, and acknowledges the unnatural pathway to developing a natural speech delivery.

Partial synchronization in the second-order Kuramoto model: An auxiliary system method.

Partial synchronization emerges in an oscillator network when the network splits into clusters of coherent and incoherent oscillators. Here, we analyze the stability of partial synchronization in the second-order finite-dimensional Kuramoto model of heterogeneous oscillators with inertia. Toward this goal, we develop an auxiliary system method that is based on the analysis of a two-dimensional piecewise-smooth system whose trajectories govern oscillating dynamics of phase differences between oscillators in the coherent cluster. Through a qualitative bifurcation analysis of the auxiliary system, we derive explicit bounds that relate the maximum natural frequency mismatch, inertia, and the network size that can support stable partial synchronization. In particular, we predict threshold-like stability loss of partial synchronization caused by increasing inertia. Our auxiliary system method is potentially applicable to cluster synchronization with multiple coherent clusters and more complex network topology.

Microstructural characterization of 15-5PH stainless steel processed by laser powder-bed fusion

The 15-5PH (UNS S 15500) stainless steel combines high mechanical strength, ductility, and good corrosion resistance for aircraft and aerospace applications. This set of properties and its high added-value applications make it an excellent choice for additive manufacturing processes such as laser powder-bed fusion (LPBF). However, there is a need to understand the complex microstructure developed in LPBF-processed parts, which may show particularities such as columnar solidification, preferential orientation, different kinds of porosities, chemical segregation along the melt pools, metastable phases, and oxide nanoinclusions. We report the microstructural characterization of LPBF-processed 15-5PH stainless steel in the as-built condition and after aging. Low porosity (<1%), high hardness (420 HV0.1), and a large amount of retained austenite (15%) were found in the as-built samples. The microstructure shows the usual “fish scale”-like morphology. Grain size and hardness vary depending on the location within the melt pools. Reconstruction of the parent grains from EBSD maps indicates a microstructural refinement due to in situ reaustenitization of parts of the previous consolidated layers, where these heat-affected zones are harder and present larger amounts of retained austenite. After aging, as-built samples were harder and more resistant to overaging than annealed or wrought counterparts. Transmission electron microscopy reveals a large amount of nanometric crystalline silicon-oxide inclusions, indexed as cristobalite. The combination of fine-grained martensite, coherent Cu-rich clusters, nanometric oxide particles, and retained austenite makes LPBF-processed 15-5PH stainless steel a very promising material for high-end structural applications.

Coherent cluster ordering in Fe-xAl and Fe-xGa alloys

The evolution of structural phases and the morphology of the microstructure of several Fe-xAl and Fe-xGa compositions were studied by neutron diffraction with high Δd/d resolution and with high-intensity continuous scanning in a wide temperature range. It was found that the formation of an ordered structure upon a change in the Al or Ga content or during a phase transition upon a change in temperature leads to a decrease in the unit-cell parameter with a “jump” of the order of Δa/a ~ 0.001. A specific microstructure in the form of mesoscopic clusters (L ~ 200–1000 Å) with an ordered atomic structure dispersedly incorporated into a disordered or less ordered matrix can be formed in the ranges of 23 at%< x < 33 at% for Fe-xAl and 19 at%< x < 24 at% for Fe-xGa. Independent determination of the unit-cell parameters of the matrix and clusters showed their coherence, which is manifested in their coincidence or proximity with a high degree of accuracy (Δa/a ≤ 0.0001). This type of phase separation (matrix + clusters) has a completely different nature with an incoherent phase coexisting in the outer or thin layers, which leads to lattice parameters difference at the level of Δa/a ~ 0.001.

Genome and Methylome analysis of a phylogenetic novel Campylobacter coli cluster with C. jejuni introgression.

The intriguing recent discovery of Campylobacter coli strains, especially of clade 1, that (i) possess mosaic C. coli / C. jejuni alleles, (ii) demonstrate mixed multilocus sequence types (MLSTs) and (iii) have undergone genome-wide introgression has led to the speculation that these two species may be involved in an accelerated rate of horizontal gene transfer that is progressively leading to the merging of both species in a process coined ‘despeciation’. In an MLST-based neighbour-joining tree of a number of C. coli and C. jejuni isolates of different clades, three prominent Campylobacter isolates formed a seemingly separate cluster besides the previously described C. coli and C. jejuni clades. In the light of the suspected, ongoing genetic introgression between the C. coli and C. jejuni species, this cluster of Campylobacter isolates is proposed to present one of the hybrid clonal complexes in the despeciation process of the genus. Specific DNA methylation as well as restriction modification systems are known to be involved in selective uptake of external DNA and their role in such genetic introgression remains to be further investigated. In this study, the phylogeny and DNA methylation of these putative C. coli / C. jejuni hybrid strains were explored, their genomic mosaic structure caused by C. jejuni introgression was demonstrated and basic phenotypic assays were used to characterize these isolates. The genomes of the three hybrid Campylobacter strains were sequenced using PacBio SMRT sequencing, followed by methylome analysis by Restriction-Modification Finder and genome analysis by Parsnp, Smash++ and blast. Additionally, the strains were phenotypically characterized with respect to growth behaviour, motility, eukaryotic cell invasion and adhesion, autoagglutination, biofilm formation, and water survival ability. Our analyses show that the three hybrid Campylobacter strains are clade 1 C . coli strains, which have acquired between 8.1 and 9.1 % of their genome from C. jejuni . The C. jejuni genomic segments acquired are distributed over the entire genome and do not form a coherent cluster. Most of the genes originating from C. jejuni are involved in chemotaxis and motility, membrane transport, cell signalling, or the resistance to toxic compounds such as bile acids. Interspecies gene transfer from C. jejuni has contributed 8.1–9.1% to the genome of three C. coli isolates and initiated the despeciation between C. jejuni and C. coli . Based on their functional annotation, the genes originating from C. jejuni enable the adaptation of the three strains to an intra-intestinal habitat. The transfer of a fused type II restriction-modification system that recognizes the CAYNNNNNCTC/GAGNNNNNRTG motif seems to be the key for the recombination of the C. jejuni genetic material with C. coli genomes.

Emergent colloidal currents across ordered and disordered landscapes

Many-particle effects in driven systems far from equilibrium lead to a rich variety of emergent phenomena. Their classification and understanding often require suitable model systems. Here we show that microscopic magnetic particles driven along ordered and defective lattices by a traveling wave potential display a nonlinear current-density relationship, which arises from the interplay of two effects. The first one originates from particle sizes nearly commensurate with the substrate in combination with attractive pair interactions. It governs the colloidal current at small densities and leads to a superlinear increase. We explain such effect by an exactly solvable model of constrained cluster dynamics. The second effect is interpreted to result from a defect-induced breakup of coherent cluster motion, leading to jamming at higher densities. Finally, we demonstrate that a lattice gas model with parallel update is able to capture the experimental findings for this complex many-body system.

Spatially Coherent Clustering Based on Orthogonal Nonnegative Matrix Factorization.

Classical approaches in cluster analysis are typically based on a feature space analysis. However, many applications lead to datasets with additional spatial information and a ground truth with spatially coherent classes, which will not necessarily be reconstructed well by standard clustering methods. Motivated by applications in hyperspectral imaging, we introduce in this work clustering models based on Orthogonal Nonnegative Matrix Factorization (ONMF), which include an additional Total Variation (TV) regularization procedure on the cluster membership matrix to enforce the needed spatial coherence in the clusters. We propose several approaches with different optimization techniques, where the TV regularization is either performed as a subsequent post-processing step or included into the clustering algorithm. Finally, we provide a numerical evaluation of 12 different TV regularized ONMF methods on a hyperspectral dataset obtained from a matrix-assisted laser desorption/ionization imaging measurement, which leads to significantly better clustering results compared to classical clustering models.

Enhancing the classification of aphasia: a statistical analysis using connected speech

ABSTRACT Background: Large-shared databases and automated language analyses allow for the application of new data analysis techniques that can shed new light on the connected speech of people with aphasia (PWA). Aims: To identify coherent clusters of PWA based on language output using unsupervised statistical algorithms and to identify features that are most strongly associated with those clusters. Methods & Procedures: Clustering and classification methods were applied to language production data from 168 PWA. Language samples were from a standard discourse protocol tapping four genres: free speech personal narratives, picture descriptions, Cinderella storytelling, and procedural discourse. Outcomes & Results: Seven distinct clusters of PWA were identified by the K-means algorithm. Using the random forest algorithm, a classification tree was proposed and validated, showing 91% agreement with the cluster assignments. This representative tree used only two variables to divide the data into distinct groups: total words from free speech tasks and total closed-class words from the Cinderella storytelling task. Conclusion: Connected speech data can be used to distinguish PWA into coherent groups, providing insight into traditional aphasia classifications, factors that may guide discourse research and clinical work.

Inverse centrifugal effect induced by collective motion of vortices in rotating thermal convection

When a fluid system is subject to strong rotation, centrifugal fluid motion is expected, i.e., denser (lighter) fluid moves outward (inward) from (toward) the axis of rotation. Here we demonstrate, both experimentally and numerically, the existence of an unexpected outward motion of warm and lighter vortices in rotating thermal convection. This anomalous vortex motion occurs under rapid rotations when the centrifugal buoyancy is sufficiently strong to induce a symmetry-breaking in the vorticity field, i.e., the vorticity of the cold anticyclones overrides that of the warm cyclones. We show that through hydrodynamic interactions the densely distributed vortices can self-aggregate into coherent clusters and exhibit collective motion in this flow regime. Interestingly, the correlation of the vortex velocity fluctuations within a cluster is scale-free, with the correlation length being proportional ( ≈ 30%) to the cluster length. Such long-range correlation leads to the counterintuitive collective outward motion of warm vortices. Our study brings insights into the vortex dynamics that are widely present in nature.

Seasonal Succession and Coherence Among Bacteria and Microeukaryotes in Lake Baikal.

Microorganisms exhibit seasonal succession governed by physicochemical factors and interspecies interactions, yet drivers of this process in different environments remain to be determined. We used high-throughput sequencing of 16S rRNA and 18S rRNA genes to study seasonal dynamics of bacterial and microeukaryotic communities at pelagic site of Lake Baikal from spring (under-ice, mixing) to autumn (direct stratification). The microbial community was subdivided into distinctive coherent clusters of operational taxonomic units (OTUs). Individual OTUs were consistently replaced during different seasonal events. The coherent clusters change their contribution to the microbial community depending on season. Changes of temperature, concentrations of silicon, and nitrates are the key factors affected the structure of microbial communities. Functional prediction revealed that some bacterial or eukaryotic taxa that switched with seasons had similar functional properties, which demonstrate their functional redundancy. We have also detected specific functional properties in different coherent clusters of bacteria or microeukaryotes, which can indicate their ability to adapt to seasonal changes of environment. Our results revealed a relationship between seasonal succession, coherency, and functional features of freshwater bacteria and microeukaryotes.

Metaphors we teach by

Abstract Teaching is a complex activity that people often discuss metaphorically, as when a professor is described as a sculptor molding impressionable students. What do such metaphors reveal about how people conceptualize teaching? Previous work has addressed related questions largely via researcher intuition and qualitative analyses of teacher attitudes. We sought to develop a more principled method for mapping the entailments of metaphorical concepts, using teaching metaphors as a case study. We presented participants with one of four common metaphors for the teacher-student relationship (identified in a preliminary study) and asked them to rate the degree to which a series of teacher attributes fit the metaphor. We then used iterated exploratory factor analysis to identify a small number of dimensions that underlie people’s conceptions of teachers and examined whether the metaphors systematically differed along these dimensions. We found that teaching metaphors bring to mind distinct, coherent clusters of teacher attributes and different intuitions about teacher responsibility and power – a finding we replicated in a larger, pre-registered follow-up study using a new set of participants. This work provides a novel method for mapping the entailments of metaphorical concepts and sets the stage for educational interventions centered on shifting lay theories of teaching.

Zr-containing precipitate evolution and its effect on the mechanical properties of Cu–Cr–Zr alloys

The present work investigates the Zr-containing precipitate evolution and its effect on the mechanical properties of a Cu–Cr–Zr alloy after solution treatment at 1253 K for 2 h and aging at 763 K for 0–6 h. The results show that the precipitation sequence of the Zr-containing precipitates in the Cu–Cr–Zr alloy is supersaturated solid solution→Zr-rich atomic clusters→Cu5Zr phase. Zr atoms first segregate at the {111} crystal plane of the copper and form coherent Zr-rich atomic clusters during the aging process, which are composed of Zr-rich atoms monolayers and exhibit plate-shaped. Some of the Zr-rich atomic clusters is transformed into the more stable phase of Cu5Zr phase as the aging time increases, the habit plane of which is the {111}Cu crystal plane. The contribution of Zr-rich atomic clusters and Cu5Zr precipitates to the yield strength of the alloy is calculated by coherency strengthening and Orowan strengthening, respectively. The total yield strength is very close to the experimentally measured strength.

A Robust Scheme for Coherency Detection in Power Systems

This paper presents an approach for online generator coherency identification based on windowed dynamic time warping (DTW). Generator rotor speed deviations measured by phasor measurement units (PMUs) are used as input data to compute a DTW dissimilarity matrix. Using the dissimilarity matrix together with Agglomerative Hierarchical Clustering (AHC) and Hubert-Levin index (C-index), generators are optimally grouped into coherent clusters. In addition to the clustering of generators, an index for characterizing the transmission delay of a Wide Area Measurement System (WAMS) is presented. A data delay factor that can indicate whether there is an inconsistent PMU data transmission delay is also proposed. The coherency identification technique and indices were tested using simulations carried out on the IEEE 39-bus system. The test results indicate that the proposed scheme accurately clusters generators into coherent groups. The suggested indices were also found to be valid. Keywords : coherence identification, dynamic time warping, speed deviation, phasor measurement unit, dissimilarity matrix