9,102 research outputs found
Mixture or mosaic? Genetic patterns in UK grey squirrels support a human-mediated ‘long-jump’ invasion mechanism
Aim Clarifying whether multiple introductions of a species remain relatively isolated or merge and interbreed is essential for understanding the dynamics of invasion processes. Multiple introductions from different sources can result in a mixture of genetically distinct populations, increasing the total genetic diversity. This mixing can resolve the ‘genetic paradox’, whereby in spite of the relatively small numbers of introduced individuals, the augmented diversity due to this mixing increases adaptability and the ability of the species to spread in new environments. Here, we aim to assess whether the expansion of a successful invader, the Eastern grey squirrel, was partly driven by the merger of multiple introductions and the effects of such a merger on diversity. Location UK, Ireland. Methods We analysed the genetic variation at 12 microsatellite loci of 381 individuals sampled from one historical and 14 modern populations of grey squirrels. Results Our data revealed that current UK population structure resembles a mosaic, with minimal interpopulation mixing and each element reflecting the genetic make-up of historic introductions. The genetic diversity of each examined population was lower than a US population or a historical UK population. Numbers of releases in a county did not correlate with county-level genetic diversity. Inbreeding coefficients remain high, and effective population sizes remain small. Main conclusions Our results support the conclusion that rapid and large-scale expansion in this species in the UK was not driven by a genetic mixing of multiple introduced populations with a single expansion front, but was promoted by repeated translocations of small propagules. Our results have implications for the management of grey squirrels and other invasive species and also demonstrate how invaders can overcome the genetic paradox, if spread is facilitated by human-mediated dispersal
Current voltage characteristics and excess noise at the trap filling transition in polyacenes
Experiments in organic semiconductors (polyacenes) evidence a strong super
quadratic increase of the current-voltage (I-V) characteristic at voltages in
the transition region between linear (Ohmic) and quadratic (trap free
space-charge-limited-current) behaviours. Similarly, excess noise measurements
at a given frequency and increasing voltages evidence a sharp peak of the
relative spectral density of the current noise in concomitance with the strong
super-quadratic I-V characteristics. Here we discuss the physical
interpretation of these experiments in terms of an essential contribution from
field assisted trapping-detrapping processes of injected carriers. To this
purpose, the fraction of filled traps determined by the I-V characteristics is
used to evaluate the excess noise in the trap filled transition (TFT) regime.
We have found an excellent agreement between the predictions of our model and
existing experimental results in tetracene and pentacene thin films of
different length in the range .Comment: 20 pg, 13 figures, in pres
Measuring the LISA test mass magnetic proprieties with a torsion pendulum
Achieving the low frequency LISA sensitivity requires that the test masses
acting as the interferometer end mirrors are free-falling with an unprecedented
small degree of deviation. Magnetic disturbances, originating in the
interaction of the test mass with the environmental magnetic field, can
significantly deteriorate the LISA performance and can be parameterized through
the test mass remnant dipole moment and the magnetic susceptibility
. While the LISA test flight precursor LTP will investigate these effects
during the preliminary phases of the mission, the very stringent requirements
on the test mass magnetic cleanliness make ground-based characterization of its
magnetic proprieties paramount. We propose a torsion pendulum technique to
accurately measure on ground the magnetic proprieties of the LISA/LTP test
masses.Comment: 6 pages, 3 figure
Characterization of disturbance sources for LISA: torsion pendulum results
A torsion pendulum allows ground-based investigation of the purity of
free-fall for the LISA test masses inside their capacitive position sensor.
This paper presents recent improvements in our torsion pendulum facility that
have both increased the pendulum sensitivity and allowed detailed
characterization of several important sources of acceleration noise for the
LISA test masses. We discuss here an improved upper limit on random force noise
originating in the sensor. Additionally, we present new measurement techniques
and preliminary results for characterizing the forces caused by the sensor's
residual electrostatic fields, dielectric losses, residual spring-like
coupling, and temperature gradients.Comment: 11 pages, 8 figures, accepted for publication Classical and Quantum
Gravit
Improved Torsion Pendulum for Ground Testing of LISA Displacement Sensors
We discuss a new torsion pendulum design for ground testing of prototype LISA
(Laser Interferometer Space Antenna) displacement sensors. This new design is
directly sensitive to net forces and therefore provides a more representative
test of the noisy forces and parasitic stiffnesses acting on the test mass as
compared to previous ground-based experiments. We also discuss a specific
application to the measurement of thermal gradient effects.Comment: 4 pages 1 figure, to appear in the Proceedings of the 10th Marcel
Grossmann Meeting on General Relativit
Hungarian International Development Cooperation: Context, Stakeholders and Performance
This paper explores the domestic and international context of Hungary's emerging international development policy. Specifically, it looks at three factors that may influence how this policy operates: membership in the European Union (EU) and potential ‘Europeanization’, Hungary's wider foreign policy strategy, and the influence of domestic stakeholders. In order to uncover how these factors affect the country's international development policy, semi-structured interviews were carried out with the main stakeholders. The main conclusions are: (1) While accession to the EU did play a crucial role in restarting Hungary's international development policy, the integration has had little effect since then; (2) international development policy seems to serve mainly Hungary's regional strategic foreign policy and economic interests, and not its global development goals; and (3) although all the domestic development stakeholders are rather weak, the Ministry of Foreign Affairs (MFA) still seems to play a dominating role. Convergence with European requirements and best practices is, therefore, clearly hindered by foreign policy interests and also by the weakness of non- governmental stakeholders
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