133 research outputs found
Fourier Method for Approximating Eigenvalues of Indefinite Stekloff Operator
We introduce an efficient method for computing the Stekloff eigenvalues
associated with the Helmholtz equation. In general, this eigenvalue problem
requires solving the Helmholtz equation with Dirichlet and/or Neumann boundary
condition repeatedly. We propose solving the related constant coefficient
Helmholtz equation with Fast Fourier Transform (FFT) based on carefully
designed extensions and restrictions of the equation. The proposed Fourier
method, combined with proper eigensolver, results in an efficient and clear
approach for computing the Stekloff eigenvalues.Comment: 12 pages, 4 figure
Infrared spectra of one- and two-dimensional fullerene polymer structures: RbC60 and rhombohedral C-60
We compare the infrared spectra of two types of fullerene polymers: the linear-chain RbC60 and the two-dimensional pressure-polymerized rhombohedral C-60. Both the splitting of the F-1u modes and the structure of newly activated Lines are in agreement with fully ordered structures of molecular symmetry D-2h and D-3d, respectively
Modified distribution in the polyphenolic profile of rosemary leaves induced by plant inoculation with an arbuscular mycorrhizal fungus
BACKGROUND: Rosemary forms an arbuscular mycorrhizal (AM) symbiosis with a group of soilborne fungi belonging to the phylum Glomeromycota, which can modify the plant metabolome responsible for the antioxidant capacity and other health beneficial properties of Rosemary. RESULTS: The effect of inoculating rosemary plants with an AM fungus on their growth via their polyphenolic fingerprinting was evaluated after analyzing leaf extracts from non-inoculated and inoculated rosemary plants by ultra-high performance liquid chromatography-high resolution mass spectrometry. . Plant growth parameters indicated that mycorrhizal inoculation significantly increased plant height and biomass. Chemical modifications in the plant polyphenolic profile distribution were found after a principal components analysis (PCA) loading plots study. Four compounds hosting strong antioxidant properties: ferulic acid, asiatic acid, carnosol, and vanillin were related to mycorrhizal rosemary plants while caffeic and chlorogenic acids had a higher influence in non-mycorrhizal plants. CONCLUSION: Mycorrhization was found to stimulate growth in order to obtain a higher biomass of plant leaves in short time and avoiding chemical fertilization, while analytical results demonstrate that there is an alteration in the distribution of polyphenols in plants colonized by the symbiotic fungus, which can be related to an improvement in nutritional properties with future industrial significanceinfo:eu-repo/semantics/acceptedVersio
Vibrational spectra of C60C8H8 and C70C8H8 in the rotor-stator and polymer phases
C60-C8H8 and C70-C8H8 are prototypes of rotor-stator cocrystals. We present
infrared and Raman spectra of these materials and show how the rotor-stator
nature is reflected in their vibrational properties. We measured the
vibrational spectra of the polymer phases poly(C60C8H8) and poly(C70C8H8)
resulting from a solid state reaction occurring on heating. Based on the
spectra we propose a connection pattern for the fullerene in poly(C60C8H8),
where the symmetry of the C60 is D2h. On illuminating the C60-C8H8 cocrystal
with green or blue light a photochemical reaction was observed leading to a
similar product to that of the thermal polymerization.Comment: 26 pages, 8 figures, to appear in Journal of Physical Chemistry B 2nd
version: minor changes in wording, accepted version by journa
Resonance energy transfer in self-organized organic/inorganic dendrite structures
Hybrid materials formed by semiconductor quantum dots and J-aggregates of cyanine dyes provide a unique combination of enhanced absorption in inorganic constituents with large oscillator strength and extremely narrow exciton bands of the organic component. The optical properties of dendrite structures with fractal dimension 1.7â1.8, formed from J-aggregates integrated with CdTe quantum dots (QDs),
have been investigated by photoluminescence spectroscopy and fluorescence lifetime imaging microscopy. Our results demonstrate that (i)J-aggregates are coupled to QDs by Fšorster-type resonant energy transfer and (ii) there are energy fluxes from the periphery to the centre of the structure, where the QD density is higher than in the periphery of the dendrite. Such an anisotropic energy transport can
be only observed when dendrites are formed from QDs integrated with J-aggregates. These QD/
J-aggregate hybrid systems can have applications in light harvesting systems and optical sensors with extended absorption spectra.Fundação para a CiĂȘncia e a Tecnologia (FCT
Degradation mechanism analysis in temperature stress tests on III-V ultra-high concentrator solar cells using a 3D distributed model
A temperature stress test was carried out on GaAs single-junction solar cells to analyze the degradation suffered when working at ultra-high concentrations. The acceleration of the degradation was realized at two different temperatures: 130 °C and 150 °C. In both cases, the degradation trend was the same, and only gradual failures were observed. A fit of the dark IâV curve at 25 °C with a 3D distributed model before and after the test was done. The fit with the 3D distributed model revealed degradation at the perimeter because the recombination current in the depletion region of the perimeter increased by about fourfold after the temperature stress test. Therefore, this test did not cause any morphological change in the devices, and although the devices were isolated with silicone, the perimeter region was revealed as the most fragile component of the solar cell. Consequently, the current flowing beneath the busbar favors the progression of defects in the device in the perimeter region
RG flows from Spin(7), CY 4-fold and HK manifolds to AdS, Penrose limits and pp waves
We obtain explicit realizations of holographic renormalization group (RG)
flows from M-theory, from E^{2,1} \times Spin(7) at UV to AdS_4 \times
\tilde{S^7} (squashed S^7) at IR, from E^{2,1} \times CY4 at UV to AdS_4 \times
Q^{1,1,1} at IR, and from E^{2,1} \times HK (hyperKahler) at UV to AdS_4 \times
N^{0,1,0} at IR. The dual type IIA string theory configurations correspond to
D2-D6 brane systems where D6 branes wrap supersymmetric four-cycles. We also
study the Penrose limits and obtain the pp-wave backgrounds for the above
configurations. Besides, we study some examples of non-supersymmetric and
supersymmetric flows in five-dimensional gauge theories.Comment: 42 pages, 6 eps figures, typos and misprints correcte
General Brane Geometries from Scalar Potentials: Gauged Supergravities and Accelerating Universes
We find broad classes of solutions to the field equations for d-dimensional
gravity coupled to an antisymmetric tensor of arbitrary rank and a scalar field
with non-vanishing potential. Our construction generates these configurations
from the solution of a single nonlinear ordinary differential equation, whose
form depends on the scalar potential. For an exponential potential we find
solutions corresponding to brane geometries, generalizing the black p-branes
and S-branes known for the case of vanishing potential. These geometries are
singular at the origin with up to two (regular) horizons. Their asymptotic
behaviour depends on the parameters of the model. When the singularity has
negative tension or the cosmological constant is positive we find
time-dependent configurations describing accelerating universes. Special cases
give explicit brane geometries for (compact and non-compact) gauged
supergravities in various dimensions, as well as for massive 10D supergravity,
and we discuss their interrelation. Some examples lift to give new solutions to
10D supergravity. Limiting cases with a domain wall structure preserve part of
the supersymmetries of the vacuum. We also consider more general potentials,
including sums of exponentials. Exact solutions are found for these with up to
three horizons, having potentially interesting cosmological interpretation. We
give several additional examples which illustrate the power of our techniques.Comment: 54 pages, 6 figures. Uses JHEP3. Published versio
Huella ambiental de carne y leche de vacuno: Manejo y emisiones
En un contexto en que el sector de la leche y la carne de vacuno estan siendo cuestionados
por su impacto ambiental, es vital medir, reducir y comunicar la huella ambiental de dichos
productos. En este sentido, IRTA ha realizado un estudio pionero en el marco del Crupo
Operativo âRumprint: huella ambiental de la carne y la leche de vacunoâ. El objetivo era
calcular la huella ambiental de estos productos, aplicando la metodologia recomendada
por la Comision Europea de âHuella Ambiental de Productoâ. Gracias a este estudio se han
podido identificar los procesos que mas contribuyen al impacto ambiental tanto de la
leche como de la carne de vacuno a lo largo de la cadena de produccion, incluyendo la
granja y todos los insumos que le Megan, hasta el envasado y distribucion de carne y leche
a centrales y supermercados.Proyecto financiado a traves de la Operacion16.01.01de Cooperacion para la innovacion del Programa de desarrollo rural de Cataluna 2014-2020 mediante fondos de la Union Europea (Europa invierte en las zonas rurales) y la Ceneralitat de Catalunya.info:eu-repo/semantics/publishedVersio
The shadow of the past: Convergence of young and old South American desert lizards as measured by head shape traits
Convergence is a pervasive phenomenon in the Tree of Life, and evolution of similar phenotypes sharing the same environmental conditions is expected in phylogenetically closely related species. In contrast, contingent factors are probably more influential in shaping phenotypic diversity for distantly related taxa. Here, we test putative convergent evolution of lizard head morphologies among relatively closely related desert dwelling Liolaemus species, and the very distantly related Ctenoblepharys adspersa. We estimated a multilocus time-calibrated phylogeny of 57 species of South American liolaemus lizards, based on seven molecular markers. We collected head shape data for 468 specimens, and used three phylogenetic comparative methods (SURFACE, CONVEVOL, and WHEATSHEAF index) to test for and estimate the strength of convergence. We found strong evidence for convergence among Pacific desert lizard C. adspersa, Liolaemus audivetulatus, Liolaemus insolitus, Liolaemus poconchilensis, Liolaemus stolzmanni, and a candidate species (Liolaemus âMoqueguaâ). Our results suggest that, despite the long divergence and phylogenetic distance of C. adspersa with respect to convergent Liolaemus species, natural selection was probably more important than historical contingency in shaping phenotypic evolution in these desert lizards.Fil: Aguilar Puntriano, CĂ©sar. Universidad Nacional Mayor de San Marcos; PerĂș. Museo de Historia Natural de San Marcos; PerĂșFil: Avila, Luciano Javier. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Centro Nacional PatagĂłnico. Instituto PatagĂłnico para el Estudio de los Ecosistemas Continentales; ArgentinaFil: de la Riva, Ignacio MarĂa. Consejo Superior de Investigaciones Cientificas. Museo Nacional de Ciencias Naturales; EspañaFil: Johnson, Leigh. University Brigham Young; Estados UnidosFil: Morando, Mariana. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Centro Nacional PatagĂłnico. Instituto PatagĂłnico para el Estudio de los Ecosistemas Continentales; ArgentinaFil: Troncoso-Palacios, Jaime. Universidad de Chile; ChileFil: Wood, Perry L.. University of Kansas; Estados UnidosFil: Sites, Jack W.. University Brigham Young; Estados Unido
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