640 research outputs found
Superconductivity emerging from an electronic phase separation in the charge ordered phase of RbFeAs
As, Rb and Rb nuclear quadrupole resonance (NQR) and
Rb nuclear magnetic resonance (NMR) measurements in RbFeAs
iron-based superconductor are presented. We observe a marked broadening of
As NQR spectrum below K which is associated with the
onset of a charge order in the FeAs planes. Below we observe a power-law
decrease in As nuclear spin-lattice relaxation rate down to K. Below that temperature the nuclei start to probe different dynamics
owing to the different local electronic configurations induced by the charge
order. A fraction of the nuclei probes spin dynamics associated with electrons
approaching a localization while another fraction probes activated dynamics
possibly associated with a pseudogap. These different trends are discussed in
the light of an orbital selective behaviour expected for the electronic
correlations.Comment: 5 pages, 3 figures and 4 pages of supplemental materia
Desymmetrization of meso ‐2,5‐Diallylpyrrolidinyl Ureas through Asymmetric Palladium‐Catalyzed Carboamination: Stereocontrolled Synthesis of Bicyclic Ureas
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/99614/1/9247_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/99614/2/anie_201302720_sm_miscellaneous_information.pd
An energy tunable continuous 23S1 positronium beam
We describe the experimental production of a beam of 23S1 positronium (Ps) atoms obtained from charge-exchange collisions between a positron beam and Xe held in a gas cell. The angular divergence of the emitted Ps beam was recorded using two position sensitive detectors located at different distances from the gas cell. The fraction of the Ps beam produced in the 23S1 level was measured via the change in the Ps count rate after driving the 23S1 → 23P2 transition with microwave radiation; with optimal experimental parameters, we estimate that up to 10% of the Ps beam is formed in the 23S1 state. The measured properties of the beam were used to evaluate the feasibility of using the system for precision spectroscopy of the n = 2 Ps fine structure using Ramsey interferometry
Dynamic Stall Computations of a Double-Swept Rotor Blade with Rigid and Elastic Modelling
Innovative helicopter rotor blades with a combined forward-backward double-sweep at the outer part of the blade enable a reduction in noise emission and enhance the overall performance of a rotor. In this context, the influence of the aeroelastic behaviour in connection with the dynamic stall phenomenon is of great importance. It is accompanied by large aerodynamic load peaks, primarily seen in the lift and the pitching moment, impacting the structural integrity of the blades and adjacent control components. Double-swept model rotor blades were developed and investigated experimentally at the DLR Göttingen regarding the dynamic stall behaviour in a four-bladed rotor configuration at the Rotor Test Facility Göttingen. Due to an axial inflow to the rotor disc a sinusoidal variation in pitch angle is introduced to trigger the dynamic stall phenomenon once per revolution. The following numerical study simulates the conducted experiments utilizing two different blade modelling approaches: elastic and rigid bodies. The corresponding computations are carried out with the use of computational fluid dynamics (CFD) and a multibody system (MBS). With the inclusion of blade elasticity both domains are connected together by using a strong aeroelastic coupling scheme. Three test cases with a rotor speed of 23.6 Hz will be presented
comprising two test cases with fixed collective pitch angle and one with a superposed cyclic variation in pitch angle in order to introduce the dynamic stall phenomenon. Finally, a comparison is carried out with experimental data including the measured rotor thrust as well as the displacements at the blade tips
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