1,383 research outputs found
Radiation Damping in the Photoionization of Fe^{14+}
A theoretical investigation of photoabsorption and photoionization of
Fe^{14+} extending beyond an earlier frame transformation R-matrix
implementation is performed using a fully-correlated, Breit-Pauli R-matrix
formulation including both fine-structure splitting of strongly-bound
resonances and radiation damping. The radiation damping of
resonances gives rise to a resonant photoionization cross section that is
significantly lower than the total photoabsorption cross section. Furthermore,
the radiation-damped photoionization cross section is found to be in good
agreement with recent experimental results once a global shift in energy of
eV is applied. These findings have important implications.
Firstly, the presently available synchrotron experimental data are applicable
only to photoionization processes and not to photoabsorption; the latter is
required in opacity calculations. Secondly, our computed cross section, for
which the L-shell ionization threshold is aligned with the NIST value, shows a
series of Rydberg resonances that are uniformly 3-4 eV
higher in energy than the corresponding experimental profiles, indicating that
the L-shell threshold energy values currently recommended by NIST are likely in
error.Comment: 4 pages, 1 figures, and 2 table
Removal of anionic surfactant from aqueous solutions by adsorption onto biochars:characterisation, kinetics, and mechanism
Biochar, a waste biomass-derived adsorbent, holds promise for decentralised wastewater treatment. However, limited research exists on its efficacy in adsorbing anionic surfactants in wastewater. To address this, the adsorption of sodium dodecyl sulphate (SDS), a common anionic surfactant, was studied using various biochar types: rice husk biochar (RH-550 and RH-700), wheat straw biochar (WS-550 and WS-700) produced at 550°C and 700°C, wood-based biochar (OB), and activated carbon (AC) as a control. The study investigated the impact of pH (3–9), adsorbent loading (1–10 g/L), adsorbent size (<0.5–2.5 mm), contact time (5–180 min), and initial concentration (50–200 mg/L) on SDS removal. Under optimised conditions (100 mg/L SDS, 4 g/L adsorbent, 1–2 mm particle size, pH 8.3, and 180 min contact time), maximum SDS removals were RH-550 (78%), RH-700 (82.4%), WS-550 (89.5%), WS-700 (90.4%), AC (97%), and OB (88.4%). Among the tested adsorbent materials, WS-550 exhibited the highest SDS adsorption capacity at 66.23 mg/g compared to AC (80.65 mg/g), followed by RH-550 (49.75 mg/g), OB (45.87 mg/g), RH-700 (43.67 mg/g), and WS-700 (42.74 mg/g). SDS adsorption followed a pseudo-second-order kinetic model, indicating chemisorption on the adsorbent surface. The Freundlich isotherm model exhibited a better fit for the experimental data on SDS adsorption using all tested adsorbents except for RH-550. This study showed that biochars produced from agricultural and forestry residues are effective adsorbents for SDS in aqueous solutions and can be a promising sustainable and low-cost material for the treatment of greywater containing anionic surfactants (e.g. handwashing, laundry, kitchen, and bathroom greywaters)
A Comprehensive X-ray Absorption Model for Atomic Oxygen
An analytical formula is developed to represent accurately the
photoabsorption cross section of O I for all energies of interest in X-ray
spectral modeling. In the vicinity of the Kedge, a Rydberg series expression is
used to fit R-matrix results, including important orbital relaxation effects,
that accurately predict the absorption oscillator strengths below threshold and
merge consistently and continuously to the above-threshold cross section.
Further minor adjustments are made to the threshold energies in order to
reliably align the atomic Rydberg resonances after consideration of both
experimental and observed line positions. At energies far below or above the
K-edge region, the formulation is based on both outer- and inner-shell direct
photoionization, including significant shake-up and shake-off processes that
result in photoionization-excitation and double photoionization contributions
to the total cross section. The ultimate purpose for developing a definitive
model for oxygen absorption is to resolve standing discrepancies between the
astronomically observed and laboratory measured line positions, and between the
inferred atomic and molecular oxygen abundances in the interstellar medium from
XSTAR and SPEX spectral models
Síntesis, caracterización y evaluación eléctrica de circonatos de bario dopados con lantánidos trivalentes
El circonato de bario es un material oxídico con estructura de tipo perovskita que muestra alta estabilidad química tanto
en ambientes oxidantes como reductores, como en presencia de agua y dióxido de carbono; su conductividad ha permitido
examinarlo como electrolito para celdas de combustible de óxido sólido encontrando buenos resultados, con la limitante de
operar a temperaturas superiores a los 800 °C.
Diversos investigadores han propuesto que es posible mejorar su conductividad eléctrica por modifi caciones en su composición
química, en particular por dopaje con cationes trivalentes que reemplacen el circonio en el sitio B de la perovskita. En este
estudio se sintetizó el circonato de bario por el método citrato amorfo a fi n examinar la posibilidad de obtenerlo en condiciones
más favorables que las presentadas por el método de síntesis convencional (método cerámico o reacción de estado sólido).
Se preparó circonato de bario dopado con europio, gadolinio, holmio, lantano, neodimio y praseodimio; la identifi cación
de fases presentes se verifi có por difracción de rayos X (DRX), las propiedades eléctricas se examinaron por espectroscopía
de impedancias (IS) a temperaturas entre 480 y 680 °C, con miras a evaluar su potencial uso como electrolito en celdas de
combustible de óxido sólido.
Los aportes de esta investigación se han centrado en el método de síntesis; en la obtención de polvos cerámicos de circonato de
bario a temperaturas inferiores a las requeridas por el método cerámico; en la obtención de información química, estructural,
morfológica y eléctrica de los materiales sintetizados.
Se encontró la fase deseada en las condiciones de síntesis establecidas, así mismo, se aprecia un incremento signifi cativo en la
conductividad de los sólidos dopados con lantano, holmio y europio en relación al material sin dopaje alguno.Barium zirconate is an oxidic material having perovskite structure that exhibits high chemical stability in both oxidizing
and reducing environments, such as in the presence of water and carbon dioxide, its conductivity has led to consider it as a
electrolyte for solid oxide fuel cell fi nding good results, with the limitation of operating at temperatures above 800 °C.
Several researchers have proposed that it is possible to improve their electrical conductivity by changes in chemical composition,
particularly for doping with trivalent cations that replace the zirconium in B site of perovskite. In this study, barium zirconate
was synthetized by the amorphous citrate method to examine the possibility of obtaining in more favorable conditions than
those made by the conventional method of synthesis (ceramic method or solid state reaction) conditions are synthesized.
Barium zirconate doped with europium, gadolinium, holmium, lanthanum, neodymium and praseodymium was prepared,
the present phase identifi cation was verifi ed by X-ray diffraction (XRD), the electrical properties were examined by impedance
spectroscopy (IS) at temperatures between 480 and 680 °C in order to evaluate its potential use as a fuel cell electrolyte in solid oxide.
The contributions of this research has focused on the synthesis method, in the production of ceramic powders of barium
zirconate at temperatures lower than those required by the ceramic method, in obtaining chemical, structural, morphological
and electrical information of material synthesized.
The desired phase synthesis conditions set found, also, a signifi cant increase is seen in the solid conductivity of doped
lanthanum, holmium and europium zirconate of barium in relation to the material without doping
Electroosmotic Pumping Between Two Immiscible Electrical Conducting Fluids Controlled by Interfacial Phenomena
In this study, the isothermal electroosmotic flow of two immiscible electrical conducting fluids within a uniform circular microcapillary was theoretically examined. It was assumed that an annular layer of liquid adjacent to the inside wall of the capillary exists, and this in turn surrounds the inner flow of a second liquid. The theoretical analysis was performed by using the linearized Poisson-Boltzmann equations, and the momentum equations for both fluids were analytically solved. The interface between the two fluids was considered uniform, hypothesis which is only valid for very small values of the capillary number, and shear and Maxwell stresses were considered as the boundary condition. In addition, a zeta potential difference and a charge density jump were assumed at the interface. In this manner, the electroosmotic pumping is governed by the previous interfacial effects, a situation that has not previously been considered in the specialized literature. The simplified equations were nondimensionalized, and analytical solutions were determined to describe the electric potential distribution and flow field in both the fluids. The solution shows the strong influence of several dimensionless parameters, such as μr, εr, , and , and , on the volumetric flow. The parameters represent the ratio of viscosity, the ratio of electric permittivity of both fluids, the dimensionless zeta potential of the microcapillary wall, the dimensionless charge density jump and charge density between both fluids, and the electrokinetic parameters, respectively
Probability-Based Dynamic Time Warping for Gesture Recognition on RGB-D Data
Dynamic Time Warping (DTW) is commonly used in gesture recognition tasks in order to tackle the temporal length variability of gestures. In the DTW framework, a set of gesture patterns are compared one by one to a maybe infinite test sequence, and a query gesture category is recognized if a warping cost below a certain threshold is found within the test sequence. Nevertheless, either taking one single sample per gesture category or a set of isolated samples may not encode the variability of such gesture category. In this paper, a probability-based DTW for gesture recognition is proposed. Different samples of the same gesture pattern obtained from RGB-Depth data are used to build a Gaussian-based probabilistic model of the gesture. Finally, the cost of DTW has been adapted accordingly to the new model. The proposed approach is tested in a challenging scenario, showing better performance of the probability-based DTW in comparison to state-of-the-art approaches for gesture recognition on RGB-D data
Canonical Analysis of the Jackiw-Teitelboim Model in the Temporal Gauge. I. The Classical Theory
As a preparation for its quantization in the loop formalism, the
2-dimensional gravitation model of Jackiw and Teitelboim is analysed in the
classical canonical formalism. The dynamics is of pure constraints as it is
well-known. A partial gauge fixing of the temporal type being performed, the
resulting second class constraints are sorted out and the corresponding Dirac
bracket algebra is worked out. Dirac observables of this classical theory are
then calculated.Comment: 15 pages, Latex. Misprint correction
X-ray He-like ions diagnostics: New Computations for Photoionized Plasmas: I. preliminary considerations
Using the new version of the photoionization code Titan designed for
plane-parallel photoionized thick hot media, which is unprecedented from the
point of view of line transfer, we have undertaken a study of the influence of
different parameters on the He-like and H-like emission of a medium
photoionized by an X-ray source. We explain why in modelling the emitting
medium it is important to solve in a self-consistent way the thermal and
ionization equilibria and to take into account the interconnection between the
different ions. We give the equivalent widths of the sum of the He-like
triplets and the triplet intensity ratios and , for the most important
He-like ions, for a range of density, column density, and ionization parameter,
in the case of constant density media. We show that the line intensities from a
given ion can be accounted for, either by small values of both the column
density and of the ionization parameter, or by large values of both quantities,
and it is necessary to take into account several ions to disentangle these
possibilities. We show also that a "pure recombination spectrum" almost never
exists in a photoionized medium: either it is thin, and resonance lines are
formed by radiative excitation, or it is thick, and free-bound absorption
destroys the resonance photons as they undergo resonant diffusion.Comment: 19 pages, 14 figures, accepted in A &
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