628 research outputs found

    Do logarithmic proximity measures outperform plain ones in graph clustering?

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    We consider a number of graph kernels and proximity measures including commute time kernel, regularized Laplacian kernel, heat kernel, exponential diffusion kernel (also called "communicability"), etc., and the corresponding distances as applied to clustering nodes in random graphs and several well-known datasets. The model of generating random graphs involves edge probabilities for the pairs of nodes that belong to the same class or different predefined classes of nodes. It turns out that in most cases, logarithmic measures (i.e., measures resulting after taking logarithm of the proximities) perform better while distinguishing underlying classes than the "plain" measures. A comparison in terms of reject curves of inter-class and intra-class distances confirms this conclusion. A similar conclusion can be made for several well-known datasets. A possible origin of this effect is that most kernels have a multiplicative nature, while the nature of distances used in cluster algorithms is an additive one (cf. the triangle inequality). The logarithmic transformation is a tool to transform the first nature to the second one. Moreover, some distances corresponding to the logarithmic measures possess a meaningful cutpoint additivity property. In our experiments, the leader is usually the logarithmic Communicability measure. However, we indicate some more complicated cases in which other measures, typically, Communicability and plain Walk, can be the winners.Comment: 11 pages, 5 tables, 9 figures. Accepted for publication in the Proceedings of 6th International Conference on Network Analysis, May 26-28, 2016, Nizhny Novgorod, Russi

    Designing CALL for learning Chinese characters

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    Despite the enormity of its quantity, printed or written forms of Chinese characters are composed from a limited number of common components. For example, the characters for pond( ), lake( ), stream( ), river ( ), sea( ) and ocean( ) all contain a component in common, a three-dot component representing water. When this clue is explicitly highlighted to students, the learning of Chinese characters can be greatly enhanced. Using a computer to help students to develop this kind of structural awareness about language learning has not yet been thoroughly examined. This paper reports on the design of CALL software based on a pedagogic method which helps students to develop the higher order skills to analyse and categorise Chinese characters by using components. The result of the classroom experiment has shown supportive evidence on the feasibility and the need of integrating the software with an affective and contextual way of teaching Chinese characters.postprin

    Paradox of low field enhancement factor for field emission nanodiodes in relation to quantum screening effects

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    We put forward the quantum screening effect in field emission [FE] nanodiodes, explaining relatively low field enhancement factors due to the increased potential barrier that impedes the electron Fowler-Nordheim tunneling, which is usually observed in nanoscale FE experiments. We illustratively show this effect from the energy band diagram and experimentally verify it by performing the nanomanipulation FE measurement for a single P-silicon nanotip emitter (Φ = 4.94eV), with a scanning tungsten-probe anode (work function, Φ = 4.5eV) that constitutes a 75-nm vacuum nanogap. A macroscopic FE measurement for the arrays of emitters with a 17-μm vacuum microgap was also performed for a fair comparison

    Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapor Deposition

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    The strong interest in graphene has motivated the scalable production of high quality graphene and graphene devices. Since large-scale graphene films synthesized to date are typically polycrystalline, it is important to characterize and control grain boundaries, generally believed to degrade graphene quality. Here we study single-crystal graphene grains synthesized by ambient CVD on polycrystalline Cu, and show how individual boundaries between coalescing grains affect graphene's electronic properties. The graphene grains show no definite epitaxial relationship with the Cu substrate, and can cross Cu grain boundaries. The edges of these grains are found to be predominantly parallel to zigzag directions. We show that grain boundaries give a significant Raman "D" peak, impede electrical transport, and induce prominent weak localization indicative of intervalley scattering in graphene. Finally, we demonstrate an approach using pre-patterned growth seeds to control graphene nucleation, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.Comment: New version with additional data. Accepted by Nature Material

    The Role of Imported Cases and Favorable Meteorological Conditions in the Onset of Dengue Epidemics

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    Dengue/dengue hemorrhagic fever is the world's most widely spread mosquito-borne arboviral disease and threatens more than two-thirds of the world's population. Cases are mainly distributed in tropical and subtropical areas in accordance with vector habitats for Aedes aegypti and Ae. albopictus. However, the role of imported cases and favorable meteorological conditions has not yet been quantitatively assessed. This study verified the correlation between the occurrence of indigenous dengue and imported cases in the context of weather variables (temperature, rainfall, relative humidity, etc.) for different time lags in southern Taiwan. Our findings imply that imported cases have a role in igniting indigenous outbreaks, in non-endemics areas, when favorable weather conditions are present. This relationship becomes insignificant in the late phase of local dengue epidemics. Therefore, early detection and case management of imported cases through timely surveillance and rapid laboratory-diagnosis may avert large scale epidemics of dengue/dengue hemorrhagic fever. An early-warning surveillance system integrating meteorological data will be an invaluable tool for successful prevention and control of dengue, particularly in non-endemic countries

    Quantifying similarity of pore-geometry in nanoporous materials

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    In most applications of nanoporous materials the pore structure is as important as the chemical composition as a determinant of performance. For example, one can alter performance in applications like carbon capture or methane storage by orders of magnitude by only modifying the pore structure. For these applications it is therefore important to identify the optimal pore geometry and use this information to find similar materials. However, the mathematical language and tools to identify materials with similar pore structures, but different composition, has been lacking. We develop a pore recognition approach to quantify similarity of pore structures and classify them using topological data analysis. This allows us to identify materials with similar pore geometries, and to screen for materials that are similar to given top-performing structures. Using methane storage as a case study, we also show that materials can be divided into topologically distinct classes requiring different optimization strategies

    Colectomy rate in steroid-refractory colitis initially responsive to cyclosporin: a long-term retrospective cohort study

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    BACKGROUND: There is consistent evidence that 50% of patients with acute, steroid-resistant flare of ulcerative colitis (UC) may achieve remission and avoid colectomy if treated with cyclosporin (CsA). However, follow-up of the responders has shown that most of them relapse and need surgery shortly after the response. We compared the records of our CsA-treated patients with those of other groups in order to help clarify this matter. METHODS: All patients admitted consecutively to our Unit with an attack of UC and treated with CsA between January 1991 and December 1999 were studied. Patients were begun on continuously-infused CsA at 2 mg/kg/day (1991–1996), or on NEORAL at an initial dose of 5 mg/kg/day (1996–1999). The maintenance treatment included oral CsA for 3–6 months with or without azathioprine (AZA). CsA failure was defined as a relapse requiring steroids with or without progression to colectomy; the cumulative probability of relapse/colectomy was assessed by Fisher's exact tests and Kaplan-Meier analysis. RESULTS: Among the patients, 39/61 (63%) initially responded. These 39 included a fatality and 4 drop-outs (unrelated to the side-effects of CsA), leaving 34 patients for the study. Of these, 61% and 35% were colectomy-free at 1 and 7 years, respectively; the corresponding figures were 80 and 60% respectively in the subset treated with AZA, but 47% and 15% in the AZA-untreated subgroup (p= 0.0007 at 7 years). Among the 34 patients, 44% were relapse-free at 1 year, but all had relapsed at 7 years (p = 0.0635). The overall resort to colectomy was 72%, while 19% of the patients remained colectomy-free. CONCLUSION: Sixty percent of a cohort of patients with steroid-refractory colitis responded to CsA and 60% of these responders retained the colon after 1 year. These figures fell to 35% at 7 years but improved to 60% on AZA. The overall need for colectomy remains high in these patients and toxicity must be monitored
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