561 research outputs found
Hydrothermal stability of Ru/SiO2-C: A promising catalyst for biomass processing through liquid-phase reactions
In this work, structural and morphological properties of SiO2-C composite material to be used as support for catalysts in the conversion of biomass-derived oxygenated hydrocarbons, such as glycerol, were investigated in liquid water under various temperatures conditions. The results show that this material does not lose surface area, and the hot liquid water does not generate changes in the structure. Neither change in relative concentrations of oxygen functional groups nor in Si/C ratio due to hydrothermal treatment was revealed by X-ray photoelectron spectroscopy (XPS) analysis. Raman analysis showed that the material is made of a disordered graphitic structure in an amorphous silica matrix, which remains stable after hydrothermal treatment. Results of the hydrogenolysis of glycerol using a Ru/SiO2-C catalyst indicate that the support gives more stability to the active phase than a Ru/SiO2 consisting of commercial silica
Development and optimization of a method for analyzing biodiesel mixtures with non-aqueous reversed phase liquid chromatography
Biodiesel (a mixture of fatty acid esters) is normally analyzed using gas chromatography/flame ionization
detection, as specified by the ASTM D6584 and EN14105 standards. This paper proposes a binary gradient
method for analyzing biodiesel mixtures using non-aqueous reverse phase HPLC with a UV detector
capable of overcoming the drawbacks of the gas chromatographic technique normally used. The new analytical
method was developed by means of a statistical sensitivity analysis applied to the main parameters
influencing the recording, using the full factorial design method combined with the Yates algorithm and
the steepest ascent optimization procedure. The present study shows the influence of the main biodiesel
mixture separation analysis parameters. The resulting tool proved valid for analyzing not only biodiesel
but also any traces of unreacted oil
Time-resolved spectroscopy of multi-excitonic decay in an InAs quantum dot
The multi-excitonic decay process in a single InAs quantum dot is studied
through high-resolution time-resolved spectroscopy. A cascaded emission
sequence involving three spectral lines is seen that is described well over a
wide range of pump powers by a simple model. The measured biexcitonic decay
rate is about 1.5 times the single-exciton decay rate. This ratio suggests the
presence of selection rules, as well as a significant effect of the Coulomb
interaction on the biexcitonic wavefunction.Comment: one typo fixe
Sub-microsecond correlations in photoluminescence from InAs quantum dots
Photon correlation measurements reveal memory effects in the optical emission
of single InAs quantum dots with timescales from 10 to 800 ns. With above-band
optical excitation, a long-timescale negative correlation (antibunching) is
observed, while with quasi-resonant excitation, a positive correlation
(blinking) is observed. A simple model based on long-lived charged states is
presented that approximately explains the observed behavior, providing insight
into the excitation process. Such memory effects can limit the internal
efficiency of light emitters based on single quantum dots, and could also be
problematic for proposed quantum-computation schemes.Comment: 8 pages, 8 figure
Quantum filter for non-local polarization properties of photonic qubits
We present an optical filter that transmits photon pairs only if they share
the same horizontal or vertical polarization, without decreasing the quantum
coherence between these two possibilities. Various applications for
entanglement manipulations and multi-photon qubits are discussed.Comment: 7 pages, including one figure, short discussion of error sources
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Spin-flip and spin-conserving optical transitions of the nitrogen-vacancy centre in diamond
We map out the first excited state sublevel structure of single nitrogen-vacancy (NV) colour centres in diamond. The excited state is an orbital doublet where one branch supports an efficient cycling transition, while the other can simultaneously support fully allowed optical Raman spin-flip transitions. This is crucial for the success of many recently proposed quantum information applications of the NV defects. We further find that an external electric field can be used to completely control the optical properties of a single centre. Finally, a group theoretical model is developed that explains the observations and provides good physical understanding of the excited state structure
Experimental characterization of an anode-supported tubular SOFC generator fueled with hydrogen, including a principal component analysis and a multi-linear regression
Production of oriented nitrogen-vacancy color centers in synthetic diamond
The negatively charged nitrogen-vacancy (NV-) center in diamond is an
attractive candidate for applications that range from magnetometry to quantum
information processing. Here we show that only a fraction of the nitrogen
(typically < 0.5 %) incorporated during homoepitaxial diamond growth by
Chemical Vapor Deposition (CVD) is in the form of undecorated NV- centers.
Furthermore, studies on CVD diamond grown on (110) oriented substrates show a
near 100% preferential orientation of NV- centers along only the [111] and
[-1-11] directions, rather than the four possible orientations. The results
indicate that NV centers grow in as units, as the diamond is deposited, rather
than by migration and association of their components. The NV unit of the NVH-
is similarly preferentially oriented, but it is not possible to determine
whether this defect was formed by H capture at a preferentially aligned NV
center or as a complete unit. Reducing the number of NV orientations from 4
orientations to 2 orientations should lead to increased optically-detected
magnetic resonance contrast and thus improved magnetic sensitivity in
ensemble-based magnetometry.Comment: 13 Pages (inlcuding suplementary information), 4 figure
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