Spin waves in quasi-equilibrium spin systems

Using the Landau Fermi liquid theory we have discovered a new regime for the propagation of spin waves in a quasi-equilibrium spin systems. We have determined the dispersion relation for the transverse spin waves and found that one of the modes is gapless. The gapless mode corresponds to the precessional mode of the magnetization in a paramagnetic system in the absence of an external magnetic field. One of the other modes is gapped which is associated with the precession of the spin current around the internal field. The gapless mode has a quadratic dispersion leading to some interesting thermodynamic properties including a $T^{3/2}$ contribution to the specific heat. We also show that these modes make significant contributions to the dynamic structure function.Comment: 4 pages, 3 figure

Stellar Chemical Abundances: In Pursuit of the Highest Achievable Precision

The achievable level of precision on photospheric abundances of stars is a major limiting factor on investigations of exoplanet host star characteristics, the chemical histories of star clusters, and the evolution of the Milky Way and other galaxies. While model-induced errors can be minimized through the differential analysis of spectrally similar stars, the maximum achievable precision of this technique has been debated. As a test, we derive differential abundances of 19 elements from high-quality asteroid-reflected solar spectra taken using a variety of instruments and conditions. We treat the solar spectra as being from unknown stars and use the resulting differential abundances, which are expected to be zero, as a diagnostic of the error in our measurements. Our results indicate that the relative resolution of the target and reference spectra is a major consideration, with use of different instruments to obtain the two spectra leading to errors up to 0.04 dex. Use of the same instrument at different epochs for the two spectra has a much smaller effect (~0.007 dex). The asteroid used to obtain the solar standard also has a negligible effect (~0.006 dex). Assuming that systematic errors from the stellar model atmospheres have been minimized, as in the case of solar twins, we confirm that differential chemical abundances can be obtained at sub-0.01 dex precision with due care in the observations, data reduction and abundance analysis.Comment: Accepted for publication in ApJ; 13 pages, 6 figures, 7 table

Absence of Wigner Crystallization in Graphene

Graphene, a single sheet of graphite, has attracted tremendous attention due to recent experiments which demonstrate that carriers in it are described by massless fermions with linear dispersion. In this note, we consider the possibility of Wigner crystallization in graphene in the absence of external magnetic field. We show that the ratio of potential and kinetic energy is independent of the carrier density, the tuning parameter that usually drives Wigner crystallization and find out that for given material parameters (dielectric constant and Fermi velocity), Wigner crystallization is not possible. We comment on the how these results change in the presence of a strong external magnetic field.Comment: 3 pages, 1 figure,Submitted for PR

Large crowding zones in peripheral vision for briefly presented stimuli

YesWhen a target is flanked by distractors, it becomes more difficult to identify. In the periphery, this crowding effect extends over a wide range of target-flanker separations, called the spatial extent of interaction (EoI). A recent study showed that the EoI dramatically increases in size for short presentation durations (Chung & Mansfield, 2009). Here we investigate this duration-EoI relation in greater detail and show that (a) it holds even when visibility of the unflanked target is equated for different durations, (b) the function saturates for durations shorter than 30 to 80 ms, and (c) the largest EoIs represent a critical spacing greater than 50% of eccentricity. We also investigated the effect of same or different polarity for targets and flankers across different presentation durations. We found that EoIs for target and flankers having opposite polarity (one white, the other black) show the same temporal pattern as for same polarity stimuli, but are smaller at all durations by 29% to 44%. The observed saturation of the EoI for shortduration stimuli suggests that crowding follows the locus of temporal integration. Overall, the results constrain theories that map crowding zones to fixed spatial extents or to lateral connections of fixed length in the cortex.This study was supported by the ERC POSITION 324070 (PC) and a visiting professorship to Anglia Ruskin University from the Leverhulme Trust (HEB)

Ordinary and Poor People in 18th-Century Delaware

The authors and their colleagues have recently carried out excavations at three 18th-century farm sites in central Delaware. The Augustine Creek South and Thomas Dawson Sites were both occupied by ordinary property owners in the 1730 to 1770 period. The Augustine Creek North Site was occupied from about 1750 to 1810 by unknown but probably poor tenants, possibly in two chronologically separate occupations. At all three sites, architectural remains and artifact deposits were found. Analysis of these sites has focused on the question of how fully ordinary and poor people participated in the social, economic, and intellectural changes of the 19th century. The answer seems to be that they did embrace some changes, such as tea drinking, but rejected others, such as the reorganization of farms and the separation of public and private space

Pairing symmetry signatures of T1 in superconducting ferromagnets

We study the nuclear relaxation rate 1/T1 as a function of temperature for a superconducting-ferromagnetic coexistent system using a p-wave triplet model for the superconducting pairing symmetry. This calculation is contrasted with a singlet s-wave one done previously, and we see for the s-wave case that there is a Hebel-Slichter peak, albeit reduced due to the magnetization, and no peak for the p-wave case. We then compare these results to a nuclear relaxation rate experiment on UGe2 to determine the possible pairing symmetry signatures in that material. It is seen that the experimental data is inconclusive to rule out the possibility of s-wave pairing in $UGe_{2}$.Comment: 4 pages, 4 figure