The effects of tidally induced disc structure on white dwarf accretion in intermediate polars

We investigate the effects of tidally induced asymmetric disc structure on accretion onto the white dwarf in intermediate polars. Using numerical simulation, we show that it is possible for tidally induced spiral waves to propagate sufficiently far into the disc of an intermediate polar that accretion onto the central white dwarf could be modulated as a result. We suggest that accretion from the resulting asymmetric inner disc may contribute to the observed X-ray and optical periodicities in the light curves of these systems. In contrast to the stream-fed accretion model for these periodicities, the tidal picture predicts that modulation can exist even for systems with weaker magnetic fields where the magnetospheric radius is smaller than the radius of periastron of the mass transfer stream. We also predict that additional periodic components should exist in the emission from low mass ratio intermediate polars displaying superhumps.Comment: 9 pages, 5 figures, accepted for publication in MNRA

Thermal Expansion and Magnetostriction Studies of a Kondo Lattice Compound: Ceagsb2

We have investigated a single crystal of CeAgSb2 using low field ac-susceptibility, thermal expansion and magnetostriction measurements in the temperature range 1.5K to 90K. The ac-susceptibility exhibits a sharp peak at 9.7K for both B//c and B perp c due to the magnetic ordering of the Ce moment. The thermal expansion coefficient alpha, exhibits highly anisotropic behaviour between 3K and 80K : alpha is positive for dL/L perp c, but negative for dL/L // c. Furthermore, alpha (for dL/L) perp c (i.e. in ab-plane) exhibits a sharp peak at TN followed by a broad maximum at 20K, while a sharp negative peak at TN followed by a minimum at 20K has been observed for (dL/L //) the c direction. The observed maximum and minimum in alpha(T) at 20K have been attributed to the crystalline field effect on the J=5/2 state of the Ce3+ ion. The magnetostriction also exhibits anisotropic behaviour with a large magnetostriction along the c-axis. The ab-plane magnetostriction exhibits a peak at B=3.3T at 3K, which is consistent with the observed peak in the magnetoresistance measurements.Comment: 4 Pages (B5), 3 figures, submitted to SCES200

Transient LTRE analysis reveals the demographic and trait-mediated processes that buffer population growth.

Temporal variation in environmental conditions affects population growth directly via its impact on vital rates, and indirectly through induced variation in demographic structure and phenotypic trait distributions. We currently know very little about how these processes jointly mediate population responses to their environment. To address this gap, we develop a general transient life table response experiment (LTRE) which partitions the contributions to population growth arising from variation in (1) survival and reproduction, (2) demographic structure, (3) trait values and (4) climatic drivers. We apply the LTRE to a population of yellow-bellied marmots (Marmota flaviventer) to demonstrate the impact of demographic and trait-mediated processes. Our analysis provides a new perspective on demographic buffering, which may be a more subtle phenomena than is currently assumed. The new LTRE framework presents opportunities to improve our understanding of how trait variation influences population dynamics and adaptation in stochastic environments

Simulating the Fate of Polycyclic Aromatic Hydrocarbons (PAHs) in the Sunndalsfjord

Årsliste 2005As part of the ongoing discussion on remedial actions against PAH contaminated sediments in the Sunndalsfjord, the SedFlex-Tool was applied to the Sunndalsfjord system in order to investigate the magnitude PAH transport from the inner Sunndalsfjord (i.e. near Sunndalsøra) to outer fjord areas (e.g. the Tingvollfjord), concentrations of PAHs in blue mussels in the Tingvollfjord if future emissions from the Sunndal plant are assumed to be zero, and how the concentrations of PAHs in the sediments in the Sunndalsfjord and Tingvollfjord will change with time. Maine conclusions are: - The transport of PAHs from the inner Sunndalsfjord to outer fjord areas in 2000 was initially estimated to be approximately 1000 kg year-1, dominated by the flux from the contaminated sediments. - The total PAH and Benzo[a]Pyrene concentrations in blue mussels inhabiting the surface layer (0 – 5 m) in the Tingvollfjord will fall rapidly once direct emissions to the system cease. The model also demonstrated that inputs from background atmospheric and riverine sources control the long-term levels of PAHs in blue mussels, rather than remobilization of contaminants from the sediments The initial total PAH levels in sediments (surface, intermediate and deep) in the Sunndalsfjord and Tingvollfjord were estimated to be approximately 11 720 µg kg-1 and 1035 µg kg-1 respectively. The model indicated that these levels decline relatively quickly and reach levels approximately 2-3 orders of magnitude lower over the simulation periodA-T Trepark AS