Search results for "TRANSITIONS"
showing 10 items of 251 documents
Dynamical Stark Effect in the nu(2)/nu(4) Vibrational Polyad of SiH(4): Theory and Observation.
2000
We report a theoretical and experimental investigation of the dynamical Stark effect in a tetrahedral molecule, silane (SiH(4)). We use a tetrahedral formalism and Floquet theory to calculate the absorption spectra for the molecule dressed by an intense nonresonant pulsed laser. Experimentally, the dynamical Stark effect is observed for transitions of the nu(2)/nu(4) vibrational polyad of SiH(4) by means of nanosecond diode laser absorption spectroscopy and a Nd:YAG laser excitation. Copyright 2000 Academic Press.
Anomalous wave structure in magnetized materials described by non-convex equations of state
2014
Agraïments: Institute for Pure and Applied Mathematics (UCLA) 2012 program on "Computational Methods in High Energy Density Plasmas. We analyze the anomalous wave structure appearing in flow dynamics under the influence of magnetic field in materials described by non-ideal equations of state. We consider the system of magnetohydrodynamics equations closed by a general equation of state (EOS) and propose a complete spectral decomposition of the fluxes that allows us to derive an expression of the nonlinearity factor as the mathematical tool to determine the nature of the wave phenomena. We prove that the possible formation of non-classical wave structure is determined by both the thermodynam…
Towards a test of the weak equivalence principle of gravity using anti-hydrogen at CERN
2016
International audience; The aim of the GBAR (Gravitational Behavior of Antimatter at Rest) experiment is to measure the free fall acceleration of an antihydrogen atom, in the terrestrial gravitational field at CERN and therefore test the Weak Equivalence Principle with antimatter. The aim is to measure the local gravity with a 1% uncertainty which can be reduced to few parts of 10-3.
Investigation of the Δn = 0 selection rule in Gamow-Teller transitions : The β-decay of 207Hg
2019
Gamow-Teller β decay is forbidden if the number of nodes in the radial wave functions of the initial and final states is different. This Δn = 0 requirement plays a major role in the β decay of heavy neutron-rich nuclei, affecting the nucleosynthesis through the increased half-lives of nuclei on the astrophysical r-process pathway below both Z = 50 (for N > 82) and Z = 82 (for N >126). The level of forbiddenness of the Δn = 1ν1g9/2 → π0g7/2 transition has been investigated from the β− decay of the ground state of 207Hg into the single-proton-hole nucleus 207Tl in an experiment at the ISOLDE Decay Station. From statistical observational limits on possible γ-ray transitions depopulating the π0…
Study of optical and magneto processes in Rb atomic vapor layer of nanometric thickness
2012
Using a narrow-band resonant fluorescence spectra from a nano-cell with a thickness of L= [lambda]/2, and VSOP resonances formed at a thickness L =[lambda] ([lambda] is the wavelength of the resonant radiation), for the first time it was experimentally investigated the behaviour of the frequency and intensity (transition probabilities) of the atomic hyperfine structure transitions between the 85Rb, 87Rb, D1 and D2 lines Zeeman sublevels in external magnetic fields in range 5 - 7000G. The behaviour of tens of previously unstudied atomic transitions was analyzed and it is demonstrated that the intensities of these lines can both greatly increase, and decrease (tenfold). For the first time it …
Electrochemical treatment of aqueous solutions containing one or many organic pollutants at boron doped diamond anodes. Theoretical modeling and expe…
2012
The electrochemical oxidation of organics in water at boron doped diamonds (BDD) was experimentally investigated with the aim to discuss the correlations among the conversion of the pollutants and the instantaneous current efficiency ICE with the operative conditions. A simple theoretical model previously developed for the oxidation of oxalic acid accounting for the cases of mass transfer control, oxidation reaction control and mixed kinetic regimes was adopted and extended to challenge its predictive capability in the case of organics of different nature and in systems with more pollutants. A quite good agreement, between theoretical predictions and experimental data pertaining to the elec…
Phase Transitions of BiVO4 under High Pressure and High Temperature
2022
We have studied the occurrence of phase transitions in two polymorphs of BiVO4 under high-pressure and high-temperature conditions by means of X-ray diffraction measurements. The fergusonite polymorph undergoes a phase transition at 1.5(1) GPa and room temperature into a tetragonal scheelite-type structure. The same transition takes place at 523(1) K and ambient pressure. A second phase transition takes place at room temperature under compression at 16(1) GPa. The transition is from the tetragonal scheelite structure to a monoclinic structure (space group P21/c). All observed phase transitions are reversible. The zircon polymorph counterpart also transforms under compression into the scheel…
Short Photoluminescence Lifetimes Linked to Crystallite Dimensions, Connectivity, and Perovskite Crystal Phases.
2022
Time-correlated single photon counting has been conducted to gain further insights into the short photoluminescence lifetimes (nanosecond) of lead iodide perovskite (MAPbI3) thin films (∼100 nm). We analyze three different morphologies, compact layer, isolated island, and connected large grain films, from 14 to 300 K using a laser excitation power of 370 nJ/cm2. Lifetime fittings from the Generalized Berberan-Santos decay model range from 0.5 to 6.5 ns, pointing to quasi-direct bandgap emission despite the three different sample strains. The high energy band emission for the isolated-island morphology shows fast recombination rate centers up to 4.8 ns–1, compared to the less than 2 ns–1 for…
Stability and nature of the volume collapse of ε-FeO under extreme conditions
2018
Iron oxides are among the major constituents of the deep Earth's interior. Among them, the epsilon phase of FeO is one of the less studied polymorphs and there is a lack of information about its structural, electronic and magnetic transformations at extreme conditions. Here we report the precise determination of its equation of state and a deep analysis of the evolution of the polyhedral units under compression, thanks to the agreement between our experiments and ab-initio simulations. Our results indicate that this material, with remarkable magnetic properties, is stable at pressures up to 27 GPa. Above 27 GPa, a volume collapse has been observed and ascribed to a change of the local envir…
Reconfigurations in sustainability transitions : a systematic and critical review
2021
Two streams of literature have become especially prominent in understanding social change toward sustainability within the past decades: the research on socio-technical transitions and applications of social practice theory. The aim of this article is to contribute to efforts to create dialogue between these two approaches. We do this by focusing on the concept of reconfiguration, which has become a much-used, but poorly defined notion in the discussion on sustainability transitions. To understand what is defined as reconfiguration in systems and practices, and how the understanding of reconfiguration in regimes could benefit from insights about reconfiguration in practices, we conducted a …