8,701 research outputs found
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
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
Microstructured superhydrorepellent surfaces: Effect of drop pressure on fakir-state stability and apparent contact angles
In this paper we present a generalized Cassi-Baxter equation to take into
account the effect of drop pressure on the apparent contact angle theta_{app}.
Also we determine the limiting pressure p_{W} which causes the impalement
transition to the Wenzel state and the pull-off pressure p_{out} at which the
drop detaches from the substrate. The calculations have been carried out for
axial-symmetric pillars of three different shapes: conical, hemispherical
topped and flat topped cylindrical pillars. Calculations show that, assuming
the same pillar spacing, conical pillars may be more incline to undergo an
impalement transition to the Wenzel state, but, on the other hand, they are
characterized by a vanishing pull-off pressure which causes the drop not to
adhere to the substrate and therefore to detach very easily. We infer that this
property should strongly reduce the contact angle hysteresis as experimentally
osberved in Ref. \cite{Martines-Conical-Shape}. It is possible to combine large
resistance to impalement transition (i.e. large value of p_{W}) and small (or
even vanishing) detaching pressure p_{out} by employing cylindrical pillars
with conical tips. We also show that depending on the particular pillar
geometry, the effect of drop pressure on the apparent contact angle theta_{app}
may be more or less significant. In particular we show that in case of conical
pillars increasing the drop pressure causes a significant decrease of
theta_{app} in agreement with some experimental investigations
\cite{LafunaTransitio}, whereas theta_{app} slightly increases for
hemispherical or flat topped cylindrical pillars.Comment: 21 pages, 13 figure
Integral group actions on symmetric spaces and discrete duality symmetries of supergravity theories
For a split, simply connected, semisimple Lie group of rank
and the maximal compact subgroup of , we give a method for computing
Iwasawa coordinates of using the Chevalley generators and the Steinberg
presentation. When is a scalar coset for a supergravity theory in
dimensions , we determine the action of the integral form
on . We give explicit results for the action of the
discrete --duality groups and on the
scalar cosets and
for type IIB supergravity
in ten dimensions and 11--dimensional supergravity in dimensions,
respectively. For the former, we use this to determine the discrete U--duality
transformations on the scalar sector in the Borel gauge and we describe the
discrete symmetries of the dyonic charge lattice. We determine the
spectrum--generating symmetry group for fundamental BPS solitons of type IIB
supergravity in dimensions at the classical level and we propose an
analog of this symmetry at the quantum level. We indicate how our methods can
be used to study the orbits of discrete U--duality groups in general
Universal law for waiting internal time in seismicity and its implication to earthquake network
In their paper (Europhys. Lett., 71 (2005) 1036), Carbone, Sorriso-Valvo,
Harabaglia and Guerra showed that "unified scaling law" for conventional
waiting times of earthquakes claimed by Bak et al. (Phys. Rev. Lett., 88 (2002)
178501) is actually not universal. Here, instead of the conventional time, the
concept of the internal time termed the event time is considered for
seismicity. It is shown that, in contrast to the conventional waiting time, the
waiting event time obeys a power law. This implies the existence of temporal
long-range correlations in terms of the event time with no sharp decay of the
crossover type. The discovered power-law waiting event-time distribution turns
out to be universal in the sense that it takes the same form for seismicities
in California, Japan and Iran. In particular, the parameters contained in the
distribution take the common values in all these geographical regions. An
implication of this result to the procedure of constructing earthquake networks
is discussed.Comment: 21 pages, 5 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
Orchestrating Forest Policy in Italy: Mission Impossible?
In the Italian political and economic agenda the forest sector occupies a marginal role. The forest sector in Italy is characterized by a high institutional fragmentation and centralized decision-making processes dominated by Public Forest Administrations. Public participation in forest policy processes has been implemented since the 1990s at national, regional and local levels in several cases. However, today no significant changes have been observed in the overall governance of the forest sector and stakeholders' involvement in Italian forest policy decision-making is still rather limited. The aims of this paper are to describe the state of forest-related participatory processes in Italy at various levels (national, regional and local) and identify which factors and actors hinder or support the establishment and implementation of participatory forest-related processes in the country. The forest-related participatory processes are analyzed adopting a qualitative-based approach and interpreting interactive, complex and non-linear participatory processes through the lens of panarchy theory
The Paths to Choreography Extraction
Choreographies are global descriptions of interactions among concurrent
components, most notably used in the settings of verification (e.g., Multiparty
Session Types) and synthesis of correct-by-construction software (Choreographic
Programming). They require a top-down approach: programmers first write
choreographies, and then use them to verify or synthesize their programs.
However, most existing software does not come with choreographies yet, which
prevents their application.
To attack this problem, we propose a novel methodology (called choreography
extraction) that, given a set of programs or protocol specifications,
automatically constructs a choreography that describes their behavior. The key
to our extraction is identifying a set of paths in a graph that represents the
symbolic execution of the programs of interest. Our method improves on previous
work in several directions: we can now deal with programs that are equipped
with a state and internal computation capabilities; time complexity is
dramatically better; we capture programs that are correct but not necessarily
synchronizable, i.e., they work because they exploit asynchronous
communication
Confined optical phonon modes in polar tetrapod nanocrystals detected by resonant inelastic light scattering
We investigated CdTe nanocrystal tetrapods of different sizes by resonant
inelastic light scattering at room temperature and under cryogenic conditions.
We observe a strongly resonant behavior of the phonon scattering with the
excitonic structure of the tetrapods. Under resonant conditions we detect a set
of phonon modes that can be understood as confined longitudinal-optical
phonons, surface-optical phonons, and transverse-optical phonons in a nanowire
picture.Comment: 12 pages, 4 figure
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