25 research outputs found
Formalism for obtaining nuclear momentum distributions by the Deep Inelastic Neutron Scattering technique
We present a new formalism to obtain momentum distributions in condensed
matter from Neutron Compton Profiles measured by the Deep Inelastic Neutron
Scattering technique. The formalism describes exactly the Neutron Compton
Profiles as an integral in the momentum variable . As a result we obtain a
Volterra equation of the first kind that relates the experimentally measured
magnitude with the momentum distributions of the nuclei in the sample. The
integration kernel is related with the incident neutron spectrum, the total
cross section of the filter analyzer and the detectors efficiency function. A
comparison of the present formalism with the customarily employed approximation
based on a convolution of the momentum distribution with a resolution function
is presented. We describe the inaccuracies that the use of this approximation
produces, and propose a new data treatment procedure based on the present
formalism.Comment: 11 pages, 8 figure
Repulsion of Single-well Fundamental Edge Magnetoplasmons in Double Quantum Wells
A {\it microscopic} treatment of fundamental edge magnetoplasmons (EMPs)
along the edge of a double quantum well (DQW) is presented for strong magnetic
fields, low temperatures, and total filling factor \nu=2. It is valid for
lateral confining potentials that Landau level (LL) flattening can be
neglected. The cyclotron and Zeeman energies are assumed larger than the DQW
energy splitting \sqrt{\Delta^2 +4T^2}, where \Delta is the splitting of the
isolated wells and T the tunneling matrix element. %hen calculated unperturbed
density profile is sharp at the edge. Using a random-phase approximation (RPA),
which includes local and nonlocal contributions to the current density, it is
shown that for negligible tunnel coupling 2T << \Delta the inter-well Coulomb
coupling leads to two DQW fundamental EMPs which are strongly renormalized in
comparison with the decoupled, single-well fundamental EMP. These DQW modes can
be modified further upon varying the inter-well distance d, along the z axis,
and/or the separation of the wells' edges \Delta y along the y axis. The charge
profile of the {\it fast} and {\it slow} DQW mode varies, respectively, in an
{\it acoustic} and {\it optical} manner along the y axis and is not smooth on
the \ell_{0} scale. For strong tunneling \Delta\alt 2T these DQW modes are
essentially modified when \Delta is changed by applying a transverse electric
field to the DQW.Comment: Text 18 pages in Latex/Revtex/Preprint format, 2 Postscript figure
Methods to improve the sample quality of macromolecular complexes for structure determination by 3D electron cryo-microscopy.
Reconstitution of both steps of S. cerevisiae splicing with purified spliceosomal components.
Direct observation of tunneling in KDP using neutron Compton scattering
Neutron Compton Scattering measurements presented here of the momentum
distribution of hydrogen in (KDP) just above and well below the
ferroelectric transition temperature show clearly that the proton is coherent
over both sites in the in the high temperature phase, a result that invalidates
the commonly accepted order-disorder picture of the transition.
The Born-Oppenheimer potential for the hydrogen, extracted directly from data
for the first time, is consistent with neutron diffraction data, and the
vibrational spectrum is in substantial agreement with infrared absorption
measurements. The measurements are sensitive enough to detect the effect of
surrounding ligands on the hydrogen bond, and can be used to study the
systematic effect of the variation of these ligands in other hydrogen bonded
systems.Comment: 5 pages, 3 figure