Foraging along a salinity gradient:The effect of tidal inundation on site choice by Dark-Bellied Brent Geese <i>Branta bernicla</i> and Barnacle Geese <i>B. leucopsis</i>

We report on the effects of salt deposition on food plants on the foraging preferences of Dark-bellied Brent Branta bernicla and Barnacle Geese B. leucopsis in a coastal staging habitat. Within one salt-marsh plant community, dominated by Red Fescue Festuca rubra, grazing pressure by geese increased with elevation (related to mean high tide), although both standing crop and nitrogen content of the forage were highest at plots lower on the salt marsh. Salt deposition on Festuca leaves decreased with increasing surface height along the elevational gradient. The, matching of census data for three spring seasons and data on soil surface elevation revealed that flocks of Barnacle Geese forage, on average, 0.4 m higher on the salt marsh than sympatric Dark-bellied Brent Geese. 84% of the Barnacle Goose flocks were encountered in areas characterised by an inundation frequency of less than 20 during the period from February through April, whereas this applied to only 44% of the Dark-bellied Brent Goose flocks. Barnacle Geese avoided foraging on salt-marsh vegetation experimentally sprayed with seawater, showing a significant preference for untreated control plots, whereas Dark-bellied Brent Geese did not react to the treatment. Dissection of nasal glands in carcasses of both species revealed that the metabolic mass-specific weight of the nasal glands of Dark-bellied Brent Geese exceeded that of Barnacle Geese by nearly a factor four. Within this species-pair of Dark-bellied Brent and Barnacle Geese, jointly using salt-marsh staging sites in spring, Barnacle Geese appear to be physiologically constrained in their choice of foraging sites within the salinity gradient of their habitat.</p

Rapid generation of angular momentum in bounded magnetized plasma

Direct numerical simulations of two-dimensional decaying MHD turbulence in bounded domains show the rapid generation of angular momentum in nonaxisymmetric geometries. It is found that magnetic fluctuations enhance this mechanism. On a larger time scale, the generation of a magnetic angular momentum, or angular field, is observed. For axisymmetric geometries, the generation of angular momentum is absent; nevertheless, a weak magnetic field can be observed. The derived evolution equations for both the angular momentum and angular field yield possible explanations for the observed behavior

Theoretical investigation of magnetic order in ReOFeAs, Re = Ce, Pr

Density functional theory (DFT) calculations are carried out on ReOFeAs, Re = Ce, Pr, the parent compounds of the high-T$_c$ superconductors ReO$_{1-x}$F$_{x}$FeAs, in order to determine the magnetic order of the ground state. It is found that the magnetic moments on the Fe sites adopt a collinear antiferromagnetic order, similar to the case of LaOFeAs. Within the generalized gradient approximation along with Coulomb onsite repulsion (GGA+U), we show that the Re magnetic moments also adopt an antiferromagnetic order for which, within the ReO layer, same spin Re sites lie along a zigzag line perpendicular to the Fe spin stripes. While within GGA the Re 4f band crosses the Fermi level, upon inclusion of onsite Coulomb interaction the 4f band splits and moves away from the Fermi level, making ReOFeAs a Mott insulator.Comment: 5 pages, 4 figure

Wide Angle Achromatic Prism Beam Steering for Infrared Countermeasures Applications

The design and analysis of achromatic doublet prisms for use in laser beam steering is presented. The geometric relationships describing the maximum steering angle are given, as are discussions of first- and second-order dispersion reduction. Infrared (IR) material alternatives and optimum IR material characteristics for wide-angle achromatic prism beam steering are also investigated. Sixteen materials in 120 different combinations have been examined to date. For midwave IR applications it is shown that the minimum dispersion currently achievable across the full 2 to 5 μm spectrum is 1.7816 mrad at an average maximum steering angle of 45 deg. This is accomplished using LiF/ZnS doublet prisms. Several issues related to the azimuth and elevation angles into which light is steered as a function of prism rotation angles are also presented

Octet Baryon Magnetic Moments in the Chiral Quark Model with Configuration Mixing

The Coleman-Glashow sum-rule for magnetic moments is always fulfilled in the chiral quark model, independently of SU(3) symmetry breaking. This is due to the structure of the wave functions, coming from the non-relativistic quark model. Experimentally, the Coleman-Glashow sum-rule is violated by about ten standard deviations. To overcome this problem, two models of wave functions with configuration mixing are studied. One of these models violates the Coleman-Glashow sum-rule to the right degree and also reproduces the octet baryon magnetic moments rather accurately.Comment: 22 pages, RevTe

Magnetism and structure of LixCoO2 and comparison to NaxCoO2

The magnetic properties and structure of LixCoO2 for x between 0.5 and 1.0 are reported. Co4+ is found to be high-spin in LixCoO2 for x between 0.94 and 1.0 and low-spin for x between 0.50 and 0.78. Weak antiferromagnetic coupling is observed, increasing in strength as more Co4+ is introduced. At an x value of about 0.65, the temperature-independent contribution to the magnetic susceptibility and the electronic contribution to the specific heat are largest. Neutron diffraction analysis reveals that the lithium oxide layer expands perpendicular to the basal plane and the Li ions displace from their ideal octahedral sites with decreasing x. A comparison of the structures of the NaxCoO2 and LixCoO2 systems reveals that the CoO2 layer changes substantially with alkali content in the former but is relatively rigid in the latter. Further, the CoO6 octahedra in LixCoO2 are less distorted than those in NaxCoO2. We postulate that these structural differences strongly influence the physical properties in the two systems

Security considerations for Galois non-dual RLWE families

We explore further the hardness of the non-dual discrete variant of the Ring-LWE problem for various number rings, give improved attacks for certain rings satisfying some additional assumptions, construct a new family of vulnerable Galois number fields, and apply some number theoretic results on Gauss sums to deduce the likely failure of these attacks for 2-power cyclotomic rings and unramified moduli