17,119 research outputs found
Vortices and charge order in high-T_c superconductors
We theoretically investigate the vortex state of the cuprate high-temperature
superconductors in the presence of magnetic fields. Assuming the recently
derived nonlinear -model for fluctuations in the pseudogap phase, we
find that the vortex cores consist of two crossed regions of elliptic shape, in
which a static charge order emerges. Charge density wave order manifests itself
as satellites to the ordinary Bragg peaks directed along the axes of the
reciprocal copper lattice. Quadrupole density wave (bond order) satellites, if
seen, are predicted to be along the diagonals. The intensity of the satellites
should grow linearly with the magnetic field, in agreement with the result of
recent experiments
Editorial: Woody plants and forest ecosystems in a complex worldâEcological interactions and physiological functioning above and below ground
International audienc
A cryogen-free, semi-automated apparatus for bullet-dynamic nuclear polarization with improved resolution
In dissolution-dynamic nuclear polarization, a hyperpolarized solid is dissolved with a jet of hot solvent. The solution is then transferred to a secondary magnet, where spectra can be recorded with improved sensitivity. In bullet-dynamic nuclear polarization this order is reversed. Pressurized gas is used to rapidly transfer the hyperpolarized solid to the secondary magnet, and the hyperpolarized solid is dissolved only upon arrival. A potential advantage of this approach is that it may avoid excessive dilution and the associated signal loss, in particular for small sample quantities. Previously, we have shown that liquid-state NMR spectra with polarization levels of up to 30â% may be recorded within less than 1âs after the departure of the hyperpolarized solid from the polarizing magnet. The resolution of the recorded spectra however was limited. The system consumed significant amounts of liquid helium, and substantial manual work was required in between experiments to prepare for the next shot. Here, we present a new bullet-DNP (dynamic nuclear polarization) system that addresses these limitations
Multi-Dimensional Astrophysical Structural and Dynamical Analysis I. Development of a Nonlinear Finite Element Approach
A new field of numerical astrophysics is introduced which addresses the
solution of large, multidimensional structural or slowly-evolving problems
(rotating stars, interacting binaries, thick advective accretion disks, four
dimensional spacetimes, etc.). The technique employed is the Finite Element
Method (FEM), commonly used to solve engineering structural problems. The
approach developed herein has the following key features:
1. The computational mesh can extend into the time dimension, as well as
space, perhaps only a few cells, or throughout spacetime.
2. Virtually all equations describing the astrophysics of continuous media,
including the field equations, can be written in a compact form similar to that
routinely solved by most engineering finite element codes.
3. The transformations that occur naturally in the four-dimensional FEM
possess both coordinate and boost features, such that
(a) although the computational mesh may have a complex, non-analytic,
curvilinear structure, the physical equations still can be written in a simple
coordinate system independent of the mesh geometry.
(b) if the mesh has a complex flow velocity with respect to coordinate space,
the transformations will form the proper arbitrary Lagrangian- Eulerian
advective derivatives automatically.
4. The complex difference equations on the arbitrary curvilinear grid are
generated automatically from encoded differential equations.
This first paper concentrates on developing a robust and widely-applicable
set of techniques using the nonlinear FEM and presents some examples.Comment: 28 pages, 9 figures; added integral boundary conditions, allowing
very rapidly-rotating stars; accepted for publication in Ap.
Design and Performance of the CMS Pixel Detector Readout Chip
The readout chip for the CMS pixel detector has to deal with an enormous data
rate. On-chip zero suppression is inevitable and hit data must be buffered
locally during the latency of the first level trigger. Dead-time must be kept
at a minimum. It is dominated by contributions coming from the readout. To keep
it low an analog readout scheme has been adopted where pixel addresses are
analog coded. We present the architecture of the final CMS pixel detector
readout chip with special emphasis on the analog readout chain. Measurements of
its performance are discussed.Comment: 8 pages, 11 figures. Contribution to the Proceedings of the Pixel2005
Workshop, Bonn, German
Reply to the Comment by Galanakis \textit{et al} on the paper \textquotedblleft Exact bosonization for an interacting Fermi gas in arbitrary dimensions"
It is shown that the criticism presented in the Comment by Galanakis et al
\cite{1} on the paper by Efetov et al \cite{2} is irrelevant to the
bosonization approach.Comment: 2 pages, no figure
Nuclear spin polarization transfer across an organic-semiconductor interface
Motivated by Tyckoâs proposal to harness optically pumped nuclear spinpolarization for the enhancement of nuclear magnetic resonance(NMR) signals from biological macromolecules, we investigate the transfer of thermal nuclear spinpolarization between 1H or 19F in an organic overlayer and 31P at the surface of micron-sized InP particles by HartmannâHahn cross polarization. Comparison with analytic and numerical models indicates that the total quantity of polarization transferred across the semiconductor-organic interface is limited by the relatively short room-temperature 1H T1Ï (11 ms) and the slow diffusion of nuclear spinpolarization in the semiconductor.Models and spin-counting experiments indicate that we are able to transfer approximately 20% of the total nuclear spinpolarization originating in the organic overlayer to the semiconductor, supporting the feasibility of transferred optically pumped NMR
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