1,533 research outputs found
Desinfestação de erva-mate in vitro.
EVINCI. Resumo 016
Production of highly oxygenated organic molecules (HOMs) from trace contaminants during isoprene oxidation
During nucleation studies from pure isoprene oxidation in the CLOUD chamber
at the European Organization for Nuclear Research (CERN) we observed
unexpected ion signals at m∕z  =  137.133
(C10H17+) and m∕z  =  81.070
(C6H9+) with the recently developed
proton-transfer-reaction time-of-flight (PTR3-TOF) mass spectrometer
instrument. The mass-to-charge ratios of these ion signals typically
correspond to protonated monoterpenes and their main fragment. We identified
two origins of these signals: first secondary association reactions of
protonated isoprene with isoprene within the PTR3-TOF reaction chamber and
secondly [4+2] cycloaddition (Diels–Alder) of isoprene inside the gas
bottle which presumably forms the favored monoterpenes limonene and
sylvestrene, as known from literature. Under our PTR3-TOF conditions used in
2016 an amount (relative to isoprene) of 2 % is formed within the
PTR3-TOF reaction chamber and 1 % is already present in the gas bottle.
The presence of unwanted cycloaddition products in the CLOUD chamber impacts
the nucleation studies by creating ozonolysis products as the corresponding
monoterpenes and is responsible for the majority of the observed highly
oxygenated organic molecules (HOMs), which in turn leads to a significant
overestimation of both the nucleation rate and the growth rate. In order to
study new particle formation (NPF) from pure isoprene oxidation under
relevant atmospheric conditions, it is important to improve and assure the
quality and purity of the precursor isoprene. This was successfully achieved
by cryogenically trapping lower-volatility compounds such as monoterpenes
before isoprene was introduced into the CLOUD chamber.</p
Temporal decorrelation of collective oscillations in neural networks with local inhibition and long-range excitation
We consider two neuronal networks coupled by long-range excitatory
interactions. Oscillations in the gamma frequency band are generated within
each network by local inhibition. When long-range excitation is weak, these
oscillations phase-lock with a phase-shift dependent on the strength of local
inhibition. Increasing the strength of long-range excitation induces a
transition to chaos via period-doubling or quasi-periodic scenarios. In the
chaotic regime oscillatory activity undergoes fast temporal decorrelation. The
generality of these dynamical properties is assessed in firing-rate models as
well as in large networks of conductance-based neurons.Comment: 4 pages, 5 figures. accepted for publication in Physical Review
Letter
Eficiência do método de desinfestação de explantes de Ilex paraguariensis Saint hilaire por cloreto de mercúrio.
EVINCI. Resumo 009
Synchronization of Integrate and Fire oscillators with global coupling
In this article we study the behavior of globally coupled assemblies of a
large number of Integrate and Fire oscillators with excitatory pulse-like
interactions. On some simple models we show that the additive effects of pulses
on the state of Integrate and Fire oscillators are sufficient for the
synchronization of the relaxations of all the oscillators. This synchronization
occurs in two forms depending on the system: either the oscillators evolve ``en
bloc'' at the same phase and therefore relax together or the oscillators do not
remain in phase but their relaxations occur always in stable avalanches. We
prove that synchronization can occur independently of the convexity or
concavity of the oscillators evolution function. Furthermore the presence of
disorder, up to some level, is not only compatible with synchronization, but
removes some possible degeneracy of identical systems and allows new mechanisms
towards this state.Comment: 37 pages, 19 postscript figures, Latex 2
Population coding by globally coupled phase oscillators
A system of globally coupled phase oscillators subject to an external input
is considered as a simple model of neural circuits coding external stimulus.
The information coding efficiency of the system in its asynchronous state is
quantified using Fisher information. The effect of coupling and noise on the
information coding efficiency in the stationary state is analyzed. The
relaxation process of the system after the presentation of an external input is
also studied. It is found that the information coding efficiency exhibits a
large transient increase before the system relaxes to the final stationary
state.Comment: 7 pages, 9 figures, revised version, new figures added, to appear in
JPSJ Vol 75, No.
Spike-Train Responses of a Pair of Hodgkin-Huxley Neurons with Time-Delayed Couplings
Model calculations have been performed on the spike-train response of a pair
of Hodgkin-Huxley (HH) neurons coupled by recurrent excitatory-excitatory
couplings with time delay. The coupled, excitable HH neurons are assumed to
receive the two kinds of spike-train inputs: the transient input consisting of
impulses for the finite duration (: integer) and the sequential input
with the constant interspike interval (ISI). The distribution of the output ISI
shows a rich of variety depending on the coupling strength and the
time delay. The comparison is made between the dependence of the output ISI for
the transient inputs and that for the sequential inputs.Comment: 19 pages, 4 figure
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