8,564 research outputs found
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 ~, 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
- …