1,067 research outputs found

    Glycerol valorization: dehydration to acrolein over silica-supported niobia catalysts

    Get PDF
    The catalytic dehydration of glycerol to acrolein is investigated over silica-supported niobia catalysts in a continuous fixed-bed gas-phase reactor. Various supported niobia catalysts are prepared and characterized using surface analysis and spectroscopic methods (XRD, UV–Vis, XPS, N2 adsorption), as well as with ammonia adsorption microcalorimetry. Good results are obtained with initial glycerol conversions of over 70% and with 50–70% selectivity to acrolein. We investigate the influence of changing the catalyst acid strength by varying the niobia content and catalyst calcination temperature. Glycerol conversion and acrolein selectivity depend on the surface acid strength. Catalyst deactivation by coking is also observed, but simple oxidative treatment in air restores the activity of the catalysts completely

    Self-energy and Self-force in the Space-time of a Thick Cosmic String

    Get PDF
    We calculate the self-energy and self-force for an electrically charged particle at rest in the background of Gott-Hiscock cosmic string space-time. We found the general expression for the self-energy which is expressed in terms of the SS matrix of the scattering problem. The self-energy continuously falls down outward from the string's center with maximum at the origin of the string. The self-force is repulsive for an arbitrary position of the particle. It tends to zero in the string's center and also far from the string and it has a maximum value at the string's surface. The plots of the numerical calculations of the self-energy and self-force are shown.Comment: 15 pages, 4 Postscript figures, ReVTe

    A Coupled-Cluster Formulation of Hamiltonian Lattice Field Theory: The Non-Linear Sigma Model

    Get PDF
    We apply the coupled cluster method (CCM) to the Hamiltonian version of the latticised O(4) non-linear sigma model. The method, which was initially developed for the accurate description of quantum many-body systems, gives rise to two distinct approximation schemes. These approaches are compared with each other as well as with some other Hamiltonian approaches. Our study of both the ground state and collective excitations leads to indications of a possible chiral phase transition as the lattice spacing is varied.Comment: 44 Pages, 14 figures. Uses Latex2e, graphicx, amstex and geometry package

    Non-holomorphic multi-matrix gauge invariant operators based on Brauer algebra

    Full text link
    We present an orthogonal basis of gauge invariant operators constructed from some complex matrices for the free matrix field, where operators are expressed with the help of Brauer algebra. This is a generalisation of our previous work for a signle complex matrix. We also discuss the matrix quantum mechanics relevant to N=4 SYM on S^{3} times R. A commuting set of conserved operators whose eigenstates are given by the orthogonal basis is shown by using enhanced symmetries at zero coupling.Comment: 29 pages, typos corrected, references adde

    Avaliação do incremento em volume de madeira de Quassia amara L.- Simaroubaceae, em cultivo agroecolĂłgico no trĂłpico Ășmido da Costa Rica.

    Get PDF
    Quassia amara Ă© arbusto de 3 a 6 metros de altura, tendo sido retirado indiscriminadamente das florestas para extrair do caule as quassinas usadas na indĂșstria farmacĂȘutica e como inseticida em agricultura orgĂąnica. NĂŁo se tem muita informação tĂ©cnica acerca do crescimento desta espĂ©cie para subsidiar estratĂ©gias de manejo sustentado. Este trabalho tem como objetivo avaliar o crescimento de Q. amara L. em cultivo agroecolĂłgico na Costa Rica. O trabalho consistiu em realizar avaliaçÔes do desenvolvimento de indivĂ­duos de Q. amara em parcelas permanentes de mediçÔes, instaladas em meio Ă s plantaçÔes desta espĂ©cie em consĂłrcio com essĂȘncias arbĂłreas. Foram efetuadas mediçÔes de diĂąmetro do caule a 10 cm do solo e altura total. Foi observado que em função das taxas de crescimento vegetal e incrementos mĂ©dio e corrente anuais (IMA e ICA), mesmo apĂłs cinco anos de plantio, a madeira de Quassia amara para extração de quassinas nĂŁo estĂĄ pronta para colheita

    AdS Branes Corresponding to Superconformal Defects

    Full text link
    We investigate an AdS_4 x L_2 D5-brane in AdS_5 x X_5 space-time, in the context of AdS/dCFT correspondence. Here, X_5 is a Sasaki-Einstein manifold and L_2 is a submanifold of X_5. This brane has the same supersymmetry as the 3-dimensional N=1 superconformal symmetry if L_2 is a special Legendrian submanifold in X_5. In this case, this brane is supposed to correspond to a superconformal wall defect in 4-dimensional N=4 super Yang-Mills theory. We construct these new string backgrounds and show they have the correct supersymmetry, also in the case with non-trivial gauge flux on L_2. The simplest new example is AdS_4 x T^2 brane in AdS_5 x S^5. We construct the brane solution expressing the RG flow between two different defects. We also perform similar analysis for an AdS_3 x L_3 M5-brane in AdS_4 x X_7, for a weak G_2 manifold X_7 and its submanifold L_3. This system has the same supersymmetry as 2-dimensional N=(1,0) global superconformal symmetry, if L_3 is an associative submanifold.Comment: 22 pages, LaTeX, 3 figures. v2: typos corrected, references added. v3: typos correcte
    • 

    corecore