KK-Means and Gaussian Mixture Modeling with a Separation Constraint

We consider the problem of clustering with $K$-means and Gaussian mixture models with a constraint on the separation between the centers in the context of real-valued data. We first propose a dynamic programming approach to solving the $K$-means problem with a separation constraint on the centers, building on (Wang and Song, 2011). In the context of fitting a Gaussian mixture model, we then propose an EM algorithm that incorporates such a constraint. A separation constraint can help regularize the output of a clustering algorithm, and we provide both simulated and real data examples to illustrate this point.Comment: 16 pages, 6 tables, 1 figure with 3 subfigure

Fitting a Multi-modal Density by Dynamic Programming

We consider the problem of fitting a probability density function when it is constrained to have a given number of modal intervals. We propose a dynamic programming approach to solving this problem numerically. When this number is not known, we provide several data-driven ways for selecting it. We perform some numerical experiments to illustrate our methodology

Studying the Learning Environment of EL Newcomer Students in the Schooling Process

In this study, we examined the schooling process of newcomer students in secondary urban schools involving survey research with newcomers and other ELs (n=268). Additionally, we conducted focus groups with students (n=10) and educators (n=12). Through qualitative measures, we examined: (a) grade level placement, (b) content area placement, and (c) academic challenges confounded by L1 proficiency, previous academic experiences, and socio-cultural experiences among newcomers. We employed quantitative methods (e.g., Descriptive, Chi Square, Factor Analysis) to detect group differences in regard to perceptions of the classroom learning environment as a function of time in the United States. In general, the Principal Component Factor analysis yielded ten factors that accounted for 66.8% of the variance. These factors provide insight into key components for the development of effective classroom learning environments in order to serve EL newcomers in the schooling process. The implications for teaching and learning practices within the classroom and school learning environments of EL newcomers are discussed

Observation of Fermi-energy dependent unitary impurity resonances in a strong topological insulator Bi2Se3 with scanning tunneling spectroscopy

Scanning tunneling spectroscopic studies of Bi2Se3 epitaxial films on Si (111) substrates reveal highly localized unitary impurity resonances associated with non-magnetic quantum impurities. The strength of the resonances depends on the energy difference between the Fermi level ({E_F}) and the Dirac point ({E_D}) and diverges as {E_F} approaches {E_D}. The Dirac-cone surface state of the host recovers within ~ 2{\AA} spatial distance from impurities, suggesting robust topological protection of the surface state of topological insulators against high-density impurities that preserve time reversal symmetry.Comment: 6 pages, 6 figures. Accepted for fast-track publication in Solid State Communications (2012

Transformation of the Microstructure of Fe-Cr Steel during Its Production

EN 1.4016 stainless steels combine good corrosion resistance with good formability and ductility. As such, their most popular applications are related to sheet forming. During re-crystallisation of Fe-Cr steels, deviations from the desired gamma-fibre (gamma fibre, ||ND) texture promote a decrease in deep drawability. Additionally, alpha-fibre (alpha fibre, ||RD) has been found to be damaging to formability. In this study, an EN 1.4016 basic material and a modified one with optimised settings as regards to chemical composition and manufacturing process, in order to improve the formability properties, are characterised. The phase diagram, microstructure, Lankford coefficients and Electron Backscatter Diffraction (EBSD) (results confirm the evolution of texture during the processing of ferritic stainless steel. Texture is analysed by the interpretation of Orientation Distribution Function (ODF), using orientation density results for each sample obtained in the processing route. The cube ({001} ) and rotated cube ({001} ) textures dominate the crystal orientation from the slab until the intermediate annealing stage. After final annealing, there is a texture evolution in both materials; the gamma-fibre component dominates the texture, which is much more intense in modified material supported by components that show good deep drawability, {554} , and good transition from hot to cold rolling, {332} . The modified composition and process material delivers a better re-crystallisation status and, therefore, the best drawability performance.This research was funded by the "Proyectos de I + D Individuales" programme, Centro para el Desarrollo Tecnologico Industrial (CDTI), Ministerio de Economia y Competitividad from the Spanish Govermment-project "FERRINOP"

Localized magnetic states in biased bilayer and trilayer graphene

We study the localized magnetic states of impurity in biased bilayer and trilayer graphene. It is found that the magnetic boundary for bilayer and trilayer graphene presents the mixing features of Dirac and conventional fermion. For zero gate bias, as the impurity energy approaches the Dirac point, the impurity magnetization region diminishes for bilayer and trilayer graphene. When a gate bias is applied, the dependence of impurity magnetic states on the impurity energy exhibits a different behavior for bilayer and trilayer graphene due to the opening of a gap between the valence and the conduction band in the bilayer graphene with the gate bias applied. The magnetic moment and the corresponding magnetic transition of the impurity in bilayer graphene are also investigated.Comment: 16 pages,6 figure

Search for t->ch at e+e- Linear Colliders

We study the rare top-quark decay t->ch, where h is a generic Higgs boson, at a linear collider. If kinematically accessible, all models contain this decay at some level due to quark flavor mixing. Some models, such as Model III of the two-Higgs doublet model, have a tree-level top-charm-Higgs coupling, and the branching ratio is close to 0.5%. Others, such as the MSSM, have a coupling induced at one-loop, and can have a branching ratio in the range of 10^{-5} - 5x10^{-4}. We find that a linear collider of root(s) = 500 GeV and a luminosity of 500 fb^{-1} will begin to be sensitive to this range of the coupling.Comment: 12 pages, 5 figures, 2 table

Ternary aromatic and anti-aromatic clusters derived from the hypho species [Sn2Sb5]3.

Heterometallic clusters have attracted broad interests in the synthetic chemistry due to their various coordination modes and potential applications in heterogeneous catalysis. Here we report the synthesis, experimental, and theoretical characterizations of four ternary clusters ([M2(CO)6Sn2Sb5]3- (M = Cr, Mo), and [(MSn2Sb5)2]4-, (M = Cu, Ag)) in the process of capturing the hypho- [Sn2Sb5]3- in ethylenediamine (en) solution. We show that the coordination of the binary anion to transition-metal ions or fragments provides additional stabilization due to the formation of locally σ-aromatic units, producing a spherical aromatic shielding region in the cages. While in the case of [Mo2(CO)6Sn2Sb5]3- stabilization arises from locally σ-aromatic three-centre and five-centre two-electron bonds, aromatic islands in [(AgSn2Sb5)2]4- and [(CuSn2Sb5)2]4- render them globally antiaromatic. This work describes the coordination chemistry of the versatile building block [Sn2Sb5]3-, thus providing conceptual advances in the field of metal-metal bonding in clusters

A discrete MMAP for analysing the behaviour of a multi-state complex dynamic system subject to multiple events.

A complex multi-state system subject to different types of failures, repairable and/or nonrepairable, external shocks and preventive maintenance is modelled by considering a discrete Markovian arrival process with marked arrivals (D-MMAP). The internal performance of the system is composed of several degradation states partitioned into minor and major damage states according to the risk of failure. Random external events can produce failures throughout the system. If an external shock occurs, there may be an aggravation of the internal degradation, cumulative external damage or extreme external failure. The internal performance and the cumulative external damage are observed by random inspection. If major degradation is observed, the unit goes to the repair facility for preventive maintenance. If a repairable failure occurs then the system goes to corrective repair with different time distributions depending on the failure state. Time distributions for corrective repair and preventive maintenance depend on the failure state. Rewards and costs depending on the state at which the device failed or was inspected are introduced. The system is modelled and several measures of interest are built into transient and stationary regimes. A preventive maintenance policy is shown to determine the effectiveness of preventive maintenance and the optimum state of internal and cumulative external damage at which preventive maintenance should be taken into account. A numerical example is presented, revealing the efficacy of the model. Correlations between the numbers of different events over time and in non-overlapping intervals are calculated. The results are expressed in algorithmic-matrix form and are implemented computationally with Matlab.Junta de Andalucía, Spain, under the grant FQM307Ministerio de Economía y Competitividad, España, MTM2017-88708-PEuropean Regional Development Fund (ERDF