The role of elevation and soil chemistry in the distribution and ion accumulation of floral morphs of Streptanthus polygaloides Gray (Brassicaceae), a Californian nickel hyperaccumulator

Background: The flora of serpentine/ultramafic soils provides an excellent model system for the study of natural selection in plant populations. Streptanthus polygaloides is a nickel hyperaccumulator that is endemic to serpentine soils in the Sierra Nevada of California, and has four floral morphs (yellow, purple, yellow-to-purple and undulate). Aims: We investigate three hypotheses: (1) the purple morph occurs in colder, wetter climates than the yellow morph; (2) tissue–soil ionic relationships differ among morphs; and (3) morphs occur on soils with differing elemental concentrations. Methods: We queried herbarium records to investigate patterns of occurrence among the yellow and purple floral morphs, and analysed soil and tissue samples from wild populations of all four morphs. Results: The purple morph inhabited serpentine outcrops with colder temperatures and greater precipitation levels than the yellow morph. Concentrations of elements in leaf tissue and rhizosphere soil differed little among populations of the morphs, but showed substantial within-site variation. Conclusions: Our results suggest that a climatic gradient may be responsible for divergence in floral colour among populations of S. polygaloides. Because of the large within-site variation in soil and tissue elemental concentrations, plants appear to have a varied physiological response to edaphic factors, regardless of morph membership

On Measuring Condensate Fraction in Superconductors

An analysis of off-diagonal long-range order in superconductors shows that the spin-spin correlation function is significantly influenced by the order if the order parameter is anisotropic on a microscopic scale. Thus, magnetic neutron scattering can provide a direct measurement of the condensate fraction of a superconductor. It is also argued that recent measurements in high temperature superconductors come very close to achieving this goal.Comment: 4 pages, 1 eps figure, RevTex. A new possibility in the underdoped regime is added. Other corrections are mino

Galaxy Counts, Sizes, Colours and Redshifts in the Hubble Deep Field

We compare the galaxy evolution models of Bruzual & Charlot (1993) with the faint galaxy count, size and colour data from the Hubble and Herschel Deep Fields (Metcalfe et al 1996). For qo=0.05, we find that models where the SFR increases exponentially out to z>2 are consistent with all of the observational data. For qo=0.5, such models require an extra population of galaxies which are only seen at high redshift and then rapidly fade or disappear. We find that, whatever the cosmology, the redshift of the faint blue galaxies and hence the epoch of galaxy formation is likely to lie at z>2. We find no implied peak in the SFR at z=1 and we suggest that the reasons for this contradiction with the results of Madau et al (1996) include differences in faint galaxy photometry, in the treatment of spiral dust and in the local galaxy count normalisation.Comment: 8 pages, 5 eps figures, needs paspconf.st

Mount St. Helens aerosol evolution

Stratospheric aerosol samples were collected using a wire impactor during the year following the eruption of Mount St. Helens. Analysis of samples shows that aerosol volume increased for 6 months due to gas-to-particle conversion and then decreased to background levels in the following 6 months

The Afterglow and Environment of the Short GRB111117A

We present multi-wavelength observations of the afterglow of the short GRB111117A, and follow-up observations of its host galaxy. From rapid optical and radio observations we place limits of r \gtrsim 25.5 mag at \deltat \approx 0.55 d and F_nu(5.8 GHz) < 18 \muJy at \deltat \approx 0.50 d, respectively. However, using a Chandra observation at t~3.0 d we locate the absolute position of the X-ray afterglow to an accuracy of 0.22" (1 sigma), a factor of about 6 times better than the Swift-XRT position. This allows us to robustly identify the host galaxy and to locate the burst at a projected offset of 1.25 +/- 0.20" from the host centroid. Using optical and near-IR observations of the host galaxy we determine a photometric redshift of z=1.3 (+0.3,-0.2), one of the highest for any short GRB, and leading to a projected physical offset for the burst of 10.5 +/- 1.7 kpc, typical of previous short GRBs. At this redshift, the isotropic gamma-ray energy is E_{gamma,iso} \approx 3\times10^51 erg (rest-frame 23-2300 keV) with a peak energy of E_{pk} \approx 850-2300 keV (rest-frame). In conjunction with the isotropic X-ray energy, GRB111117A appears to follow our recently-reported E_x,iso-E_gamma,iso-E_pk universal scaling. Using the X-ray data along with the optical and radio non-detections we find that for a blastwave kinetic energy of E_{K,iso} \approx E_{gamma,iso}, the circumburst density is n_0 \sim 3x10^(-4)-1 cm^-3 (for a range of epsilon_B=0.001-0.1). Similarly, from the non-detection of a break in the X-ray light curve at t<3 d, we infer a minimum opening angle for the outflow of theta_j> 3-10 degrees (depending on the circumburst density). We conclude that Chandra observations of short GRBs are effective at determining precise positions and robust host galaxy associations in the absence of optical and radio detections.Comment: ApJ accepted versio

Observation of Pure Spin Transport in a Diamond Spin Wire

Spin transport electronics - spintronics - focuses on utilizing electron spin as a state variable for quantum and classical information processing and storage. Some insulating materials, such as diamond, offer defect centers whose associated spins are well-isolated from their environment giving them long coherence times; however, spin interactions are important for transport, entanglement, and read-out. Here, we report direct measurement of pure spin transport - free of any charge motion - within a nanoscale quasi 1D 'spin wire', and find a spin diffusion length ~ 700 nm. We exploit the statistical fluctuations of a small number of spins ($\sqrt{N}$ < 100 net spins) which are in thermal equilibrium and have no imposed polarization gradient. The spin transport proceeds by means of magnetic dipole interactions that induce flip-flop transitions, a mechanism that can enable highly efficient, even reversible, pure spin currents. To further study the dynamics within the spin wire, we implement a magnetic resonance protocol that improves spatial resolution and provides nanoscale spectroscopic information which confirms the observed spin transport. This spectroscopic tool opens a potential route for spatially encoding spin information in long-lived nuclear spin states. Our measurements probe intrinsic spin dynamics at the nanometre scale, providing detailed insight needed for practical devices which seek to control spin.Comment: 7 pages, 2 figures, under consideration at Nature Nanotechnolog

Magnetic resonance at 41 meV and charge dynamics in YBa_2Cu_3O_6.95

We report an Eliashberg analysis of the electron dynamics in YBa_2Cu_3O_6.95. The magnetic resonance at 41 meV couples to charge carriers and defines the characteristic shape in energy of the scattering rate \tau^{-1}(T,\omega) which allows us to construct the charge-spin spectral density I^2\chi(\omega,T) at temperature T. The T dependence of the weight under the resonance peak in I^2\chi(\omega,T) agrees with experiment as does that of the London penetration depth and of the microwave conductivity. Als, at T=0 condensation energy, the fractional oscillator strength in the condensate, and the ratio of gap to critical temperature agree well with the data.Comment: 7 Pages, 3 Figures, accepted for publication in Europhysics Letter

Zeeman Anisotropy Fluorescence Spectroscopy, Characteristic Radiative Lifetimes, and Novel Site Symmetries in KCl: Sm 2+

By means of Zeeman anisotropy fluorescence (ZAF) and its field dependence (up to 55.8 kG), the authors have investigated the 4.2 K narrow-line fluorescence of KCl:Sm2+ and identified some hitherto unreported Sm2+ sites. The strong no-field line at 7693.5 Å (5D0→7F3) and a very weak no-field line at 8742.8 Å (5D0→7F5) are shown to be of C3v symmetry origin. The 24.5-kG ZAF pattern observed in the 7696-7700-Å (5D0→7F3) region has been identified to originate from a type-II Cs site. The 26.5-kG ZAF patterns of the C3v no-field line at 7693.5 Å and the type-I Cs no-field line at 7694.5 Å overlap in the 7693-7695.3-Å region, and are elucidated through the field dependence of their Zeeman components. Characteristic radiative lifetimes of the 5D0 level in several Sm2+ symmetry types have been determined from dominant transitions to the 7FJ (J\u3c~4) levels. There are two distinct C4v sites: one with a lifetime of 9.5 msec, and the other 11.2 msec. C2v and type-I Cs sites have lifetimes of 10.5 and 10.8 msec, respectively, which are indistinguishable within the experimental error. The role of O2− compensation of Sm2+ in addition to K+ vacancy compensation in KCl is discussed in terms of these findings