Evidence for Skyrmion crystallization from NMR relaxation experiments

A resistively detected NMR technique was used to probe the two-dimensional electron gas in a GaAs/AlGaAs quantum well. The spin-lattice relaxation rate $(1/T_{1})$ was extracted at near complete filling of the first Landau level by electrons. The nuclear spin of $^{75}$As is found to relax much more efficiently with $T\to 0$ and when a well developed quantum Hall state with $R_{xx}\simeq 0$ occurs. The data show a remarkable correlation between the nuclear spin relaxation and localization. This suggests that the magnetic ground state near complete filling of the first Landau level may contain a lattice of topological spin texture, i.e. a Skyrmion crystal

Distinct high-T transitions in underdoped Ba1−x_{1-x}Kx_{x}Fe2_{2}As2_{2}

In contrast to the simultaneous structural and magnetic first order phase transition $T_{0}$ previously reported, our detailed investigation on an underdoped Ba$_{0.84}$K$_{0.16}$Fe$_{2}$As$_{2}$ single crystal unambiguously revealed that the transitions are not concomitant. The tetragonal ($\tau$: I4/mmm) - orthorhombic ($\vartheta$: Fmmm) structural transition occurs at $T_{S}\simeq$ 110 K, followed by an adjacent antiferromagnetic (AFM) transition at $T_{N}\simeq$ 102 K. Hysteresis and coexistence of the $\tau$ and $\vartheta$ phases over a finite temperature range observed in our NMR experiments confirm the first order character of the structural transition and provide evidence that both $T_{S}$ and $T_{N}$ are strongly correlated. Our data also show that superconductivity (SC) develops in the $\vartheta$ phase below $T_{c}$ = 20 K and coexists with long range AFM. This new observation, $T_{S}\neq T_{N}$, firmly establishes another similarity between the hole-doped BaFe$_{2}$As$_{2}$ via K substitution and the electron-doped iron-arsenide superconductors.Comment: 4 pages, 3 figure

Periodic orbits in the restricted three-body problem and Arnold's J+J^+-invariant

We apply Arnold's theory of generic smooth plane curves to Stark-Zeeman systems. This is a class of Hamiltonian dynamical systems that describes the dynamics of an electron in an external electric and magnetic field, and includes many systems from celestial mechanics. Based on Arnold's $J^+$-invariant, we introduce invariants of periodic orbits in planar Stark-Zeeman systems and study their behaviour.Comment: 36 Pages, 16 Figure

The origin of green icebergs in Antarctica

A comparison of samples from a translucent green iceberg with a core from the Ronne Ice Shelf revealed an excellent agreement in isotopic composition, crystal structure, and incorporated sediment particles. Marine shelf ice which constitutes the basal portion of some ice shelves is considered to be the source of green icebergs. It most likely results from "ice pump" processes which produce large amounts of ice platelets in the water column beneath ice shelves. These subsequently accumulate and become compacted into bubble-free, desalinated ice. Iceberg and drift-buoy trajectories indicate that green icebergs observed in the Weddell Sea originate from the Amery Ice Shelf rather than from the Ronne Ice Shelf, although the latter ice shelf is also a potential source

Magnetic field independence of the spin gap in YBa_2Cu_3O_{7-delta}

We report, for magnetic fields of 0, 8.8, and 14.8 Tesla, measurements of the temperature dependent ^{63}Cu NMR spin lattice relaxation rate for near optimally doped YBa_2Cu_3O_{7-delta}, near and above T_c. In sharp contrast with previous work we find no magnetic field dependence. We discuss experimental issues arising in measurements of this required precision, and implications of the experiment regarding issues including the spin or pseudo gap.Comment: 4 pages, 3 figures, as accepted for publication in Physical Review Letter

Opinions of UK rescue shelter and rehoming center workers on the problems facing their industry

Animal shelters exist worldwide to care for and rehome unwanted or straying pets. Previous studies have examined why owners breed unwanted animals, or relinquish their pets to shelters. However, the views of shelter workers, who receive and care for these animals, have previously been largely unexplored. The aim of this study was to investigate the perceptions of animal shelter workers on the problems facing their industry. A sampling frame was constructed, consisting of every identified shelter in the UK, and a postal questionnaire sent to each. This included two open questions, soliciting respondents’ views on their biggest problems, and inviting further comments. A total of 661 respondents replied to at least one question. Thematic analysis on the free text content was carried out, and basic and global themes identified. Respondents’ main concerns centered on a mismatch between the continuous demand for their services and their limited resources, which has worsened during the recent financial crisis. Respondents perceived a need for increased public awareness of the commitment involved in keeping a pet, and of controlling breeding by neutering. Points of intervention, such as education programs, were suggested. Coordinating efforts with others, including local authorities, landlords, and housing associations, and a potential role for veterinary professionals working in shelter medicine were all explored by respondents. Rehoming organizations play an important role in the management of pet overpopulation, and the views and beliefs of their workers form an important contribution to the dialogue surrounding this issue. Consideration of these perspectives may suggest alternative routes to address underlying causes and management of pet overpopulation