Hierarchical modelling of temperature and habitat size effects on population dynamics of North Atlantic cod

Understanding how temperature affects cod (Gadus morhua) ecology is important for forecasting how populations will develop as climate changes in future. The effects of spawning-season temperature and habitat size on cod recruitment dynamics have been investigated across the North Atlantic. Ricker and Beverton and Holt stock–recruitment (SR) models were extended by applying hierarchical methods, mixed-effects models, and Bayesian inference to incorporate the influence of these ecosystem factors on model parameters representing cod maximum reproductive rate and carrying capacity. We identified the pattern of temperature effects on cod productivity at the species level and estimated SR model parameters with increased precision. Temperature impacts vary geographically, being positive in areas where temperatures are <5°C, and negative for higher temperatures. Using the relationship derived, it is possible to predict expected changes in population-specific reproductive rates and carrying capacities resulting from temperature increases. Further, carrying capacity covaries with available habitat size, explaining at least half its variability across stocks. These patterns improve our understanding of environmental impacts on key population parameters, which is required for an ecosystem approach to cod management, particularly under ocean-warming scenarios. Key words: carrying capacity , cod , hierarchical models , North Atlantic , temperature , uncertaint

Dispersion relations for stationary light in one-dimensional atomic ensembles

We investigate the dispersion relations for light coupled to one-dimensional ensembles of atoms with different level schemes. The unifying feature of all the considered setups is that the forward and backward propagating quantum fields are coupled by the applied classical drives such that the group velocity can vanish in an effect known as "stationary light". We derive the dispersion relations for all the considered schemes, highlighting the important differences between them. Furthermore, we show that additional control of stationary light can be obtained by treating atoms as discrete scatterers and placing them at well defined positions. For the latter purpose, a multi-mode transfer matrix theory for light is developed

Doppler cooling of calcium ions using a dipole-forbidden transition

Doppler cooling of calcium ions has been experimentally demonstrated using the S1/2 to D5/2 dipole-forbidden transition. Scattering forces and fluorescence levels a factor of 5 smaller than for usual Doppler cooling on the dipole allowed S1/2 to P1/2 transition have been achieved. Since the light scattered from the ions can be monitored at (violet) wavelengths that are very different from the excitation wavelengths, single ions can be detected with an essentially zero background level. This, as well as other features of the cooling scheme, can be extremely valuable for ion trap based quantum information processing.Comment: 4 pages, 4 figures, minor changes to commentary and reference

Vascular access to the arterial side of the pancreas in the Syrian hamster

In order to establish a new approach to the treatment of tumours of the exocrine pancreas of humans, this work was aimed at gaining vascular access to the arterial side of the pancreas in the Syrian hamster. There is to our knowledge no information available in the literature concerning the catheterisation of the arterial side of the pancreas in the Syrian hamster. Preliminary anatomical studies revealed that the coeliac artery could be a possible vascular access to the different lobes of the pancreas in the Syrian hamster. The lumen of the splenic artery is too small to be catheterised. Injection of Evan´s blue and plastic beads in different sizes into the coelic artery demonstrated distribution to the different lobes of the pancreas as well as to the spleen, the stomach, the duodenum, and the omentum.This opens up the possibility of a treatment, using biodegradable plastic beads coated with immunomodulators injected on the arterial side of the pancreas, as well as alginate beads harbouring transfected cells, capable of delivering various substances in the area of interest

Screening model for nanowire surface-charge sensors in liquid

The conductance change of nanowire field-effect transistors is considered a highly sensitive probe for surface charge. However, Debye screening of relevant physiological liquid environments challenge device performance due to competing screening from the ionic liquid and nanowire charge carriers. We discuss this effect within Thomas-Fermi and Debye-Huckel theory and derive analytical results for cylindrical wires which can be used to estimate the sensitivity of nanowire surface-charge sensors. We study the interplay between the nanowire radius, the Thomas-Fermi and Debye screening lengths, and the length of the functionalization molecules. The analytical results are compared to finite-element calculations on a realistic geometry.Comment: 4 pages including 2 figures. Accepted for AP

Towards low-dimensional hole systems in Be-doped GaAs nanowires

GaAs was central to the development of quantum devices but is rarely used for nanowire-based quantum devices with InAs, InSb and SiGe instead taking the leading role. p-type GaAs nanowires offer a path to studying strongly-confined 0D and 1D hole systems with strong spin-orbit effects, motivating our development of nanowire transistors featuring Be-doped p-type GaAs nanowires, AuBe alloy contacts and patterned local gate electrodes towards making nanowire-based quantum hole devices. We report on nanowire transistors with traditional substrate back-gates and EBL-defined metal/oxide top-gates produced using GaAs nanowires with three different Be-doping densities and various AuBe contact processing recipes. We show that contact annealing only brings small improvements for the moderately-doped devices under conditions of lower anneal temperature and short anneal time. We only obtain good transistor performance for moderate doping, with conduction freezing out at low temperature for lowly-doped nanowires and inability to reach a clear off-state under gating for the highly-doped nanowires. Our best devices give on-state conductivity 95 nS, off-state conductivity 2 pS, on-off ratio ~$10^{4}$, and sub-threshold slope 50 mV/dec at T = 4 K. Lastly, we made a device featuring a moderately-doped nanowire with annealed contacts and multiple top-gates. Top-gate sweeps show a plateau in the sub-threshold region that is reproducible in separate cool-downs and indicative of possible conductance quantization highlighting the potential for future quantum device studies in this material system