1,844 research outputs found
Super-expanders and warped cones
For a Banach space , we show that any family of graphs quasi-isometric to levels of a warped cone is an expander with respect to if and only if the induced -representation on has a spectral gap. This provides examples of graphs that are an expander with respect to all Banach spaces of non-trivial type
How Future Space-Based Weak Lensing Surveys Might Obtain Photometric Redshifts Independently
We study how the addition of on-board optical photometric bands to future
space-based weak lensing instruments could affect the photometric redshift
estimation of galaxies, and hence improve estimations of the dark energy
parameters through weak lensing. Basing our study on the current proposed
Euclid configuration and using a mock catalog of galaxy observations, various
on-board options are tested and compared with the use of ground-based
observations from the Large Synoptic Survey Telescope (LSST) and Pan-STARRS.
Comparisons are made through the use of the dark energy Figure of Merit, which
provides a quantifiable measure of the change in the quality of the scientific
results that can be obtained in each scenario. Effects of systematic offsets
between LSST and Euclid photometric calibration are also studied. We find that
adding two (U and G) or even one (U) on-board optical band-passes to the
space-based infrared instrument greatly improves its photometric redshift
performance, bringing it close to the level that would be achieved by combining
observations from both space-based and ground-based surveys while freeing the
space mission from reliance on external datasets.Comment: Accepted for publication in PASP. A high-quality version of Fig 1 can
be found on http://www.ap.smu.ca/~sawicki/DEphoto
Quantitative Determination of the Adiabatic Condition Using Force-Detected Nuclear Magnetic Resonance
The adiabatic condition governing cyclic adiabatic inversion of proton spins
in a micron-sized ammonium chloride crystal was studied using room temperature
nuclear magnetic resonance force microscopy. A systematic degradation of
signal-to-noise was observed as the adiabatic condition became violated. A
theory of adiabatic following applicable to cyclic adiabatic inversion is
reviewed and implemented to quantitatively determine an adiabaticity threshold
from our experimental results.Comment: 5 pages, 3 fig
Thickness dependence of magnetic properties of (Ga,Mn)As
We report on a monotonic reduction of Curie temperature in dilute
ferromagnetic semiconductor (Ga,Mn)As upon a well controlled
chemical-etching/oxidizing thinning from 15 nm down to complete removal of the
ferro- magnetic response. The effect already starts at the very beginning of
the thinning process and is accompanied by the spin reorientation transition of
the in-plane uniaxial anisotropy. We postulate that a negative gradient along
the growth direction of self-compensating defects (Mn interstitial) and the
presence of surface donor traps gives quantitative account on these effects
within the p-d mean field Zener model with adequate mod- ifications to take a
nonuniform distribution of holes and Mn cations into account. The described
here effects are of practical importance for employing thin and ultrathin
layers of (Ga,Mn)As or relative compounds in concept spintronics devices, like
resonant tunneling devices in particular.Comment: 4 pages, 4 figures and supplementary information 2 pages, 1 figur
- …