1,222 research outputs found
Maser Oscillation in a Whispering-Gallery-Mode Microwave Resonator
We report the first observation of above-threshold maser oscillation in a
whispering-gallery(WG)-mode resonator, whose quasi-transverse-magnetic, 17th
azimuthal-order WG mode, at a frequency of approx. 12.038 GHz, with a loaded Q
of several hundred million, is supported on a cylinder of mono-crystalline
sapphire. An electron spin resonance (ESR) associated with Fe3+ ions, that are
substitutively included within the sapphire at a concentration of a few parts
per billion, coincides in frequency with that of the (considerably narrower) WG
mode. By applying a c.w. `pump' to the resonator at a frequency of approx.
31.34 GHz, with no applied d.c. magnetic field, the WG (`signal') mode is
energized through a three-level maser scheme. Preliminary measurements
demonstrate a frequency stability (Allan deviation) of a few times 1e-14 for
sampling intervals up to 100 s.Comment: REVTeX v.4, 3 pages, with a separate .bbl file and 3 .eps figure
Comparison of 7T 16-channel Dual-row Transmit Arrays
We evaluated and compared the performance of an inductively decoupled and overlapped dual-row transmit arrays for MRI at 7T. For the evaluated designs, the coupling between adjacent elements in the same row was higher for the overlapped compared to the non-overlapped configuration. However the transmit efficiencies for the circular polarization mode of both coils were similar. For comparisons of array transmit performance, consideration of array-internal losses as well as reflected and radiated power is very important, because their sum can be as high as 55% of the total transmit power
Creating traveling waves from standing waves from the gyrotropic paramagnetic properties of Fe ions in a high-Q whispering gallery mode sapphire resonator
We report observations of the gyrotropic change in magnetic susceptibility of
the Fe electron paramagnetic resonance at 12.037GHz (between spin states
and ) in sapphire with respect to applied magnetic field.
Measurements were made by observing the response of the high-Q Whispering
Gallery doublet (WGH) in a Hemex sapphire resonator cooled to 5
K. The doublets initially existed as standing waves at zero field and were
transformed to traveling waves due to the gyrotropic response.Comment: Accepted for publication in Phys. Rev.
fMRI protocol optimization for simultaneously studying small subcortical and cortical areas at 7 T
Neutron Correlations in the Decay of the First Excited State of 11Li
The decay of unbound excited 11Li was measured after being populated by a two-proton removal from a 13B beam at 71 MeV/nucleon. Decay energy spectra and Jacobi plots were obtained from measurements of the momentum vectors of the 9Li fragment and neutrons. A resonance at an excitation energy of âŒ1.2 MeV was observed. The kinematics of the decay are equally well fit by a simple dineutron-like model or a phase-space model that includes final state interactions. A sequential decay model can be excluded
Spectroscopy of Ti and the systematic behavior of low energy octupole states in Ca and Ti isotopes
Excited states of the nucleus Ti have been studied, via both
inverse-kinematics proton scattering and one-neutron knockout from Ti by
a liquid hydrogen target, using the GRETINA -ray tracking array.
Inelastic proton-scattering cross sections and deformation lengths have been
determined. A low-lying octupole state has been tentatively identified in
Ti for the first time. A comparison of results on low-energy
octupole states in the neutron-rich Ca and Ti isotopes with the results of
Random Phase Approximation calculations demonstrates that the observed
systematic behavior of these states is unexpected.Comment: 7 pages, 8 figure
Spectroscopy of Ti and the systematic behavior of low energy octupole states in Ca and Ti isotopes
Excited states of the nucleus Ti have been studied, via both
inverse-kinematics proton scattering and one-neutron knockout from Ti by
a liquid hydrogen target, using the GRETINA -ray tracking array.
Inelastic proton-scattering cross sections and deformation lengths have been
determined. A low-lying octupole state has been tentatively identified in
Ti for the first time. A comparison of results on low-energy
octupole states in the neutron-rich Ca and Ti isotopes with the results of
Random Phase Approximation calculations demonstrates that the observed
systematic behavior of these states is unexpected.Comment: 7 pages, 8 figure
Grande vitesse ferroviaire et développement économique local : une revue de la littérature
Octupole strength in the neutron-rich calcium isotopes
Low-lying excited states of the neutron-rich calcium isotopes Ca
have been studied via -ray spectroscopy following inverse-kinematics
proton scattering on a liquid hydrogen target using the GRETINA -ray
tracking array. The energies and strengths of the octupole states in these
isotopes are remarkably constant, indicating that these states are dominated by
proton excitations.Comment: 15 pages, 3 figure
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