565 research outputs found
Scalable Spatial Framework for NoSQL Databases - Haslam Scholars Program Undergraduate Thesis
The spatial frameworks used for knowledge discovery in “Big Data” areas such as urban information systems (UIS) are well- developed in SQL databases but are not as extensive within certain NoSQL databases. The focus of this project is to develop this framework for emerging search systems (ESS) in UIS by utilizing NoSQL databases, notably the document-based MongoDB. Such framework includes spatial functions for the most fundamental spatial queries. An ESS in UIS can take advantage of these new and attractive features of scalability within MongoDB to provide a robust approach to spatial search that differs from SQL relations and scalability. MongoDB, which is relatively in its early stages of spatial search in contrast to PostgreSQL, will require contributions to its spatial “toolbox”. Many of the operations present in SQL packages, such as PostGIS, are not in MongoDB. Thus, there is an opportunity to contribute to MongoDB’s ongoing geospatial evolution by developing, testing, and optimizing the spatial utilities used for large NoSQL datasets. Within UIS, these core operations can prove to be an important starting point for detailed geospatial analysis and high-impact data production. We hope, by open sourcing this framework (as an extension), it can serve the research community as the foundation for scalable NoSQL platforms for big geospatial data analytics and be the next stage for open source contributions to MongoDB
Quasi-Exactly Solvable N-Body Spin Hamiltonians with Short-Range Interaction Potentials
We review some recent results on quasi-exactly solvable spin models
presenting near-neighbors interactions. These systems can be understood as
cyclic generalizations of the usual Calogero-Sutherland models. A nontrivial
modification of the exchange operator formalism is used to obtain several
infinite families of eigenfunctions of these models in closed form.Comment: This is a contribution to the Proc. of workshop on Geometric Aspects
of Integrable Systems (July 17-19, 2006; Coimbra, Portugal), published in
SIGMA (Symmetry, Integrability and Geometry: Methods and Applications) at
http://www.emis.de/journals/SIGMA
A Haldane-Shastry spin chain of BC_N type in a constant magnetic field
We compute the spectrum of the trigonometric Sutherland spin model of BC_N
type in the presence of a constant magnetic field. Using Polychronakos's
freezing trick, we derive an exact formula for the partition function of its
associated Haldane-Shastry spin chain.Comment: LaTeX, 13 page
Exchange operator formalism for N-body spin models with near-neighbors interactions
We present a detailed analysis of the spin models with near-neighbors
interactions constructed in our previous paper [Phys. Lett. B 605 (2005) 214]
by a suitable generalization of the exchange operator formalism. We provide a
complete description of a certain flag of finite-dimensional spaces of spin
functions preserved by the Hamiltonian of each model. By explicitly
diagonalizing the Hamiltonian in the latter spaces, we compute several infinite
families of eigenfunctions of the above models in closed form in terms of
generalized Laguerre and Jacobi polynomials.Comment: RevTeX, 31 pages, no figures; important additional conten
Tunable uptake of poly(ethylene oxide) by graphite-oxide-based materials
We investigate the role of structure and chemical composition on the uptake of poly(ethylene oxide) by a series of graphite oxides (GOs) and thermally reduced GOs, leading to the formation of polymer-intercalated GO and polymer-adsorbed graphene nanostructures. To this end, a series of poly(ethylene oxide) (PEO) - GO hybrid materials exhibiting a variable degree of GO oxidation and exfoliation has been investigated in detail using a combination of techniques including X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetry, scanning-electron microscopy, and nitrogen adsorption. Intercalation of the polymer phase into well-defined GO galleries is found to correlate well with both the degree of GO oxidation and with the presence of hydroxyl groups. The latter feature is an essential prerequisite to optimize polymer uptake owing to the predominance of hydrogen-bonding interactions between intercalant and host. Unlike the bulk polymer, these intercalation compounds show neither crystallisation nor glass-transition associated with the polymer phase. Exfoliation and reduction of GO result in high-surface-area graphene layers exhibiting the highest polymer uptake in these GO-based materials. In this case, PEO undergoes surface adsorption, where we observe the recovery of glass and melting transitions associated with the polymer phase albeit at significantly lower temperatures than the bulk
Collective excitations in liquid D2 confined within the mesoscopic pores of a MCM-41 molecular sieve
We present a comparative study of the excitations in bulk and liquid D2
confined within the pores of MCM-41. The material (Mobile Crystalline
Material-41) is a silicate obtained by means of a template that yields a
partially crystalline structure composed by arrays of nonintersecting hexagonal
channels of controlled width having walls made of amorphous SiO2. Its porosity
was characterized by means of adsorption isotherms and found to be composed by
a regular array of pores having a narrow distribution of sizes with a most
probable value of 2.45 nm. The assessment of the precise location of the sample
within the pores is carried out by means of pressure isotherms. The study was
conducted at two pressures which correspond to pore fillings above the
capillary condensation regime. Within the range of wave vectors where
collective excitations can be followed up (0.3<Q<3.0 −1), we found
confinement brings forward a large shortening of the excitation lifetimes that
shifts the characteristic frequencies to higher energies. In addition, the
coherent quasielastic scattering shows signatures of reduced diffusivity.Comment: 6 page
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