659 research outputs found
Pressure-induced transition from the dynamic to static Jahn-Teller effect in (PhP)IC
High-pressure infrared transmission measurements on \PhC60 were performed up
to 9 GPa over a broad frequency range (200 - 20000 cm) to monitor the
vibrational and electronic/vibronic excitations under pressure. The four
fundamental T modes of \C60a\ are split into doublets already at the
lowest applied pressure and harden with increasing pressure. Several cation
modes and fullerene-related modes split into doublets at around 2 GPa, the most
prominent one being the G mode. The splitting of the vibrational modes
can be attributed to the transition from the dynamic to static Jahn-Teller
effect, caused by steric crowding at high pressure. Four absorption bands are
observed in the NIR-VIS frequency range. They are discussed in terms of
transitions between LUMO electronic states in \C60a, which are split because of
the Jahn-Teller distortion and can be coupled with vibrational modes. Various
distortions and the corresponding symmetry lowering are discussed. The observed
redshift of the absorption bands indicates that the splitting of the LUMO
electronic states is reduced upon pressure application.Comment: 10 pages, 17 figure
A hyperparasite affects the population dynamics of a wild plant pathogen
Assessing the impact of natural enemies of plant and animal pathogens on their host’s
population dynamics is needed to determine the role of hyperparasites in affecting
disease dynamics, and their potential for use in efficient control strategies of patho-
gens. Here, we focus on the long-term study describing metapopulation dynamics of
an obligate pathogen, the powdery mildew (
Podosphaera plantaginis
) naturally infect-
ing its wild host plant (
Plantago lanceolata
) in the fragmented landscape of the
�
Aland
archipelago (southwest Finland). Regionally, the pathogen persists through a balance
of extinctions and colonizations, yet factors affecting extinction rates remain poorly
understood. Mycoparasites of the genus
Ampelomyces
appear as good candidates for
testing the role of a hyperparasite, i.e. a parasite of other parasites, in the regulation of
their fungal hosts’ population dynamics. For this purpose, we first designed a quantita-
tive PCR assay for detection of
Ampelomyces
spp. in field-collected samples. This
newly developed molecular test was then applied to a large-scale sampling within the
�
Aland archipelago, revealing that
Ampelomyces
is a widespread hyperparasite in this
system, with high variability in prevalence among populations. We found that the
hyperparasite was more common on leaves where multiple powdery mildew strains
coexist, a pattern that may be attributed to differential exposure. Moreover, the preva-
lence of
Ampelomyces
at the plant level negatively affected the overwinter survival of
its fungal host. We conclude that this hyperparasite may likely impact on its host pop-
ulation dynamics and argue for increased focus on the role of hyperparasites in disease
dynamics
Diffusion in normal and critical transient chaos
In this paper we investigate deterministic diffusion in systems which are
spatially extended in certain directions but are restricted in size and open in
other directions, consequently particles can escape. We introduce besides the
diffusion coefficient D on the chaotic repeller a coefficient which
measures the broadening of the distribution of trajectories during the
transient chaotic motion. Both coefficients are explicitly computed for
one-dimensional models, and they are found to be different in most cases. We
show furthermore that a jump develops in both of the coefficients for most of
the initial distributions when we approach the critical borderline where the
escape rate equals the Liapunov exponent of a periodic orbit.Comment: 4 pages Revtex file in twocolumn format with 2 included postscript
figure
Orbital Magnetism in Ensembles of Parabolic Potentials
We study the magnetic susceptibility of an ensemble of non-interacting
electrons confined by parabolic potentials and subjected to a perpendicular
magnetic field at finite temperatures. We show that the behavior of the average
susceptibility is qualitatively different from that of billiards. When averaged
over the Fermi energy the susceptibility exhibits a large paramagnetic response
only at certain special field values, corresponding to comensurate classical
frequencies, being negligible elsewhere. We derive approximate analytical
formulae for the susceptibility and compare the results with numerical
calculations.Comment: 4 pages, 4 figures, REVTE
Non-minimal Maxwell-Chern-Simons theory and the composite Fermion model
The magnetic field redefinition in Jain's composite fermion model for the
fractional quantum Hall effect is shown to be effectively described by a
mean-field approximation of a model containing a Maxwell-Chern-Simons gauge
field non-minimally coupled to matter. Also an explicit non-relativistic limit
of the non-minimal (2+1)D Dirac equation is derived.Comment: 10 pages, no figure
Migration pattern of Gambel’s White-crowned Sparrow along the Pacific Flyway
White-crowned Sparrow (Zonotrichia leucophrys) populations of western North America exhibit dramatic differences in life history strategies including migration behavior. However, individual migration strategies and population-level migratory patterns remain largely unknown for this species. Here, we focused on the long-distance migratory subspecies, Gambel’s White-crowned Sparrow (Zonotrichia leucophrys gambelii). We used ringing, tracking and stable hydrogen isotope (δ2H) analysis of individuals migrating along the Pacific Flyway to assess individual phenology and routes as well as the pattern of connectivity between breeding and non-breeding sites. Results from all three methods, consisting of 79 ring recoveries, four light level geolocator tracks and 388 feather δ2H values, indicate low degrees of migratory connectivity. The isotope data provide evidence for leapfrog migration with the more southerly populations traveling greater distances to the breeding grounds than more centrally wintering individuals. Location estimates of four annual journeys revealed individually consistent migration strategies with relatively short flight bouts separated by two to three and two to six stopover sites during spring and autumn migration, respectively. However, combined results from all methods indicate high variability in migration distance among individuals. These findings confirm the phenotypic flexibility observed within this species and highlight the potential of White-crowned Sparrows for further investigations of evolutionary adaptations to ongoing changes in the environment
Supercooled confined water and the Mode Coupling crossover temperature
We present a Molecular Dynamics study of the single particle dynamics of
supercooled water confined in a silica pore. Two dynamical regimes are found:
close to the hydrophilic substrate molecules are below the Mode Coupling
crossover temperature, , already at ambient temperature. The water closer
to the center of the pore (free water) approaches upon supercooling as
predicted by Mode Coupling Theories. For free water the crossover temperature
and crossover exponent are extracted from power-law fits to both the
diffusion coefficient and the relaxation time of the late region.Comment: To be published, Phys. Rev. Lett., 4 pages, 3 figures, revTeX, minor
changes in the figures, references added, changes in the tex
Speech-centric multimodal interaction for easy-to-access online services: A personal life assistant for the elderly
The PaeLife project is a European industry-academia collaboration whose goal is to provide the elderly with easy access to online services that make their life easier and encourage their continued participation in the society. To reach this goal, the project partners are developing a multimodal virtual personal life assistant (PLA) offering a wide range of services from weather information to social networking. This paper presents the multimodal architecture of the PLA, the services provided by the PLA, and the work done in the area of speech input and output modalities, which play a key role in the application.info:eu-repo/semantics/publishedVersio
Speech-centric multimodal interaction for easy-to-access online services: A personal life assistant for the elderly
The PaeLife project is a European industry-academia collaboration whose goal is to provide the elderly with easy access to online services that make their life easier and encourage their continued participation in the society. To reach this goal, the project partners are developing a multimodal virtual personal life assistant (PLA) offering a wide range of services from weather information to social networking. This paper presents the multimodal architecture of the PLA, the services provided by the PLA, and the work done in the area of speech input and output modalities, which play a key role in the application.info:eu-repo/semantics/publishedVersio
Anomalous Workfunction Anisotropy in Ternary Acetylides
Anomalous anisotropy of workfunction values in ternary alkali metal
transition metal acetylides is reported. Workfunction values of some
characteristic surfaces in these emerging semiconducting materials may differ
by more than 2 eV as predicted by Density Functional Theory
calculations. This large anisotropy is a consequence of the relative
orientation of rod-like [MC] negatively charged polymeric
subunits and the surfaces, with M being a transition metal or metalloid element
and C refers to the acetylide ion C, with the rods embedded
into an alkali cation matrix. It is shown that the conversion of the seasoned
CsTe photo-emissive material to ternary acetylide CsTeC
results in substantial reduction of its 3 eV workfunction down to
1.71-2.44 eV on the CsTeC(010) surface while its high quantum yield
is preserved. Similar low workfunction values are predicted for other ternary
acetylides as well, allowing for a broad range of applications from improved
electron- and light-sources to solar cells, field emission displays, detectors
and scanners.Comment: Accepted for publication in Phys. Rev.
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