78,028 research outputs found
A Study of the Structure of the Transition Metal Hydryls Final Report
Crystal and molecular structures of transition rhodium and lithium hydril
An optimal control approach to pilot/vehicle analysis and Neal-Smith criteria
The approach of Neal and Smith was merged with the advances in pilot modeling by means of optimal control techniques. While confirming the findings of Neal and Smith, a methodology that explicitly includes the pilot's objective in attitude tracking was developed. More importantly, the method yields the required system bandwidth along with a better pilot model directly applicable to closed-loop analysis of systems in any order
Entangled states of trapped ions allow measuring the magnetic field gradient of a single atomic spin
Using trapped ions in an entangled state we propose detecting a magnetic
dipole of a single atom at distance of a few m. This requires a
measurement of the magnetic field gradient at a level of about 10
Tesla/m. We discuss applications e.g. in determining a wide variation of
ionic magnetic moments, for investigating the magnetic substructure of ions
with a level structure not accessible for optical cooling and detection,and for
studying exotic or rare ions, and molecular ions. The scheme may also be used
for measureing spin imbalances of neutral atoms or atomic ensembles trapped by
optical dipole forces. As the proposed method relies on techniques well
established in ion trap quantum information processing it is within reach of
current technology.Comment: 4 pages, 2 fi
Type Ia supernova diversity: Standardizing the candles
Future use of type Ia supernovae for cosmology aims not only to determine the
equation of state of dark energy, but also to constrain possible variations in
its value. To achieve this goal, supernovae need to become better calibrated
standard candles - not only to improve the precision of the measurement, but
more importantly to gain better control over systematic uncertainties in order
to ensure the accuracy of the result.
Here we report on a project to quantify the diversity in type Ia supernovae,
and to look for trends and/or sub-types that can be used to improve their
calibration as standard candles. We implement a version of principal component
analysis on type Ia supernova spectra. Although the quantity of data is not
sufficient to draw any firm conclusions we show that this method holds promise
for, at the very least, effectively separating peculiar supernovae. Whether it
can be further used to improve the calibration of normal type Ia's remains a
project for future study.Comment: Conference Proceedings. Cefalu 2006, The multicoloured landscape of
compact objects and their explosive origins. Six pages, three figure
Triplon mean-field analysis of an antiferromagnet with degenerate Shastry-Sutherland ground states
We look into the quantum phase diagram of a spin-
antiferromagnet on the square lattice with degenerate Shastry-Sutherland ground
states, for which only a schematic phase diagram is known so far. Many exotic
phases were proposed in the schematic phase diagram by the use of exact
diagonalization on very small system sizes. In our present work, an important
extension of this antiferromagnet is introduced and investigated in the
thermodynamic limit using triplon mean-field theory. Remarkably, this
antiferromagnet shows a stable plaquette spin-gapped phase like the original
Shastry-Sutherland antiferromagnet, although both of these antiferromagnets
differ in the Hamiltonian construction and ground state degeneracy. We propose
a sublattice columnar dimer phase which is stabilized by the second and third
neighbor antiferromagnetic Heisenberg exchange interactions. There are also
some commensurate and incommensurate magnetically ordered phases, and other
spin-gapped phases which find their places in the quantum phase diagram.
Mean-field results suggest that there is always a level-crossing phase
transition between two spin gapped phases, whereas in other situations, either
a level-crossing or a continuous phase transition happens
How to measure spatial distances?
The use of time--like geodesics to measure temporal distances is better
justified than the use of space--like geodesics for a measurement of spatial
distances. We give examples where a ''spatial distance'' cannot be
appropriately determined by the length of a space--like geodesic.Comment: 4 pages, latex, no figure
- …