662 research outputs found
Argon metastable dynamics in a filamentary jet micro-discharge at atmospheric pressure
Space and time resolved concentrations of Ar () metastable atoms at
the exit of an atmospheric pressure radio-frequency micro-plasma jet were
measured using tunable diode laser absorption spectroscopy. The discharge
features a coaxial geometry with a hollow capillary as an inner electrode and a
ceramic tube with metal ring as outer electrode. Absorption profiles of
metastable atoms as well as optical emission measurements reveal the dynamics
and the filamentary structure of the discharge. The average spatial
distribution of Ar metastables is characterized with and without a target in
front of the jet, showing that the target potential and therewith the electric
field distribution substantially changes the filaments' expansion. Together
with the detailed analysis of the ignition phase and the discharge's behavior
under pulsed operation, the results give an insight into the excitation and
de-excitation mechanisms
Critical slowing down near the multiferroic phase transition in MnWO
By using broadband dielectric spectroscopy in the radiofrequency and
microwave range we studied the magnetoelectric dynamics in the multiferroic
chiral antiferromagnet MnWO. Above the multiferroic phase transition at
K we observe a critical slowing down of the corresponding
magnetoelectric fluctuations resembling the soft-mode behavior in canonical
ferroelectrics. This electric field driven excitation carries much less
spectral weight than ordinary phonon modes. Also the critical slowing down of
this mode scales with an exponent larger than one which is expected for
magnetic second order phase transition scenarios. Therefore the investigated
dynamics have to be interpreted as the softening of an electrically active
magnetic excitation, an electromagnon.Comment: 5 pages, 4 figures, appendi
Dielectric properties of charge ordered LuFe2O4 revisited: The apparent influence of contacts
We show results of broadband dielectric measurements on the charge ordered,
proposed to be mul- tiferroic material LuFe2O4. The temperature and frequency
dependence of the complex permittivity as investigated for temperatures above
and below the charge-oder transition near T_CO ~ 320 K and for frequencies up
to 1 GHz can be well described by a standard equivalent-circuit model
considering Maxwell-Wagner-type contacts and hopping induced AC-conductivity.
No pronounced contribution of intrinsic dipolar polarization could be found and
thus the ferroelectric character of the charge order in LuFe2O4 has to be
questioned.Comment: 4 pages, 3 figure
Logic Integer Programming Models for Signaling Networks
We propose a static and a dynamic approach to model biological signaling
networks, and show how each can be used to answer relevant biological
questions. For this we use the two different mathematical tools of
Propositional Logic and Integer Programming. The power of discrete mathematics
for handling qualitative as well as quantitative data has so far not been
exploited in Molecular Biology, which is mostly driven by experimental
research, relying on first-order or statistical models. The arising logic
statements and integer programs are analyzed and can be solved with standard
software. For a restricted class of problems the logic models reduce to a
polynomial-time solvable satisfiability algorithm. Additionally, a more dynamic
model enables enumeration of possible time resolutions in poly-logarithmic
time. Computational experiments are included
Wavelet analysis of vehicle door closure sounds
Wavelet analysis of vehicle door closure sound
State of Mnemiopsis leidyi (Ctenophora: Lobata) and mesozooplankton in Iranian waters of the Caspian Sea during 2008 in comparison with previous surveys
Mnemiopsis leidyi which was accidentally introduced into the Caspian Sea in 1999 and since then has colonized extensively. The horizontal distribution of M. leidyi and dominant mesozooplankton species was investigated in the south western Caspian Sea during February, May, July and November 2008. The average number and biomass of M. leidyi were in the same range (ca 200 individuals m^-3 (2000 ind m^-2)) and 16 g wet weight m^-3 (180 g m^-2) in comparison with previous surveys. As in previous years the population consisted mainly of individuals <1 cm. The decline in mesozooplankton species observed since 1996 continued in 2008. Only two species of the previously recorded 24 Cladocera species were found in 2008. Of five Copepoda species recorded in 1996, only one, Acartia tonsa, was found in 2008 and even here adult individuals have reduced 3-fold since 1996. Bivalve larvae have declined by one order of magnitude since 1996. Among the dominant species, only the numbers of Cirripedia larvae and in part the numbers of Pleopis polyphemoides (Cladocera) were in the same range as in 1996
Impurity intrusion in radio-frequency micro-plasma jets operated in ambient air
Space and time resolved concentrations of helium metastable atoms in an
atmospheric pressure radio-frequency micro-plasma jet were measured using
tunable diode laser absorption spectroscopy. Spatial profiles as well as
lifetime measurements show significant influences of air entering the discharge
from the front nozzle and of impurities originating from the gas supply system.
Quenching of metastables was used to deduce quantitative concentrations of
intruding impurities. The impurity profile along the jet axis was determined
from optical emission spectroscopy as well as their dependance on the feed gas
flow through the jet.Comment: Journal of Physics D: Applied Physics (accepted), 6 page
CdV2O4: A rare example of a collinear multiferroic spinel
By studying the dielectric properties of the geometrically frustrated spinel
CdV2O4, we observe ferroelectricity developing at the transition into the
collinear antiferromagnetic ground state. In this multiferroic spinel,
ferroelectricity is driven by local magnetostriction and not by the more common
scenario of spiral magnetism. The experimental findings are corroborated by
ab-initio calculations of the electric polarization and the underlying spin and
orbital order. The results point towards a charge rearrangement due to
dimerization, where electronic correlations and the proximity to the
insulator-metal transition play an important role.Comment: 4+ pages, 3 figure
Family Health Climate and Adolescents’ Physical Activity and Healthy Eating: A Cross-Sectional Study with Mother-Father-Adolescent Triads
The importance of the family environment for children’s and adolescents’ health behavior has been demonstrated, the underlying mechanisms of this influence remain unclear. Therefore, the aim of the study was to investigate the relationship between family environmental and individual determinants. It was hypothesized that the Family Health Climate (FHC) is associated with adolescents’ physical activity and dietary behavior and that intrinsic motivation mediates this association.
Methods
Cross-sectional data were collected from 198 families (mother, father, and child) using questionnaires. Perceptions of FHC of mothers, fathers, and their children were assessed using the FHC-scales for physical activity (FHC-PA) and nutrition (FHC-NU). The adolescents also rated their intrinsic motivation for exercise and healthy eating, their physical activity and consumption of healthful food. A structural equation model was analyzed and a bootstrapping procedure was used to test direct and indirect effects.
Results
The FHC-PA was related to the amount of weekly physical activity and the FHC-NU to the consumption of fruit, vegetables and salad. These effects were mediated by adolescents’ intrinsic motivation; the indirect effects were significant for both behaviors.
Discussion
These results emphasize the importance of the FHC in shaping adolescents’ physical activity and dietary behavior. Individual motivational factors are potential mediators of family and parental influences. Considering family-level variables and their interaction with individual factors contributes to the understanding of adolescents’ health behavior
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