858 research outputs found
On the Persistent Shape and Coherence of Pulsating Auroral Patches
The pulsating aurora covers a broad range of fluctuating shapes that are
poorly characterized. The purpose of this paper is therefore to provide
objective and quantitative measures of the extent to which pulsating auroral
patches maintain their shape, drift and fluctuate in a coherent fashion. We
present results from a careful analysis of pulsating auroral patches using
all-sky cameras. We have identified four well-defined individual patches that
we follow in the patch frame of reference. In this way we avoid the space-time
ambiguity which complicates rocket and satellite measurements. We find that the
shape of the patches is remarkably persistent with 85-100% of the patch being
repeated for 4.5-8.5 min. Each of the three largest patches has a temporal
correlation with a negative dependence on distance, and thus does not fluctuate
in a coherent fashion. A time-delayed response within the patches indicates
that the so-called streaming mode might explain the incoherency. The patches
appear to drift differently from the SuperDARN-determined
X convection velocity.
However, in a nonrotating reference frame the patches drift with 230-287 m/s in
a north eastward direction, which is what typically could be expected for the
convection return flow
Statistics of Auroral Langmuir Waves
The Physics of Auroral Zone Electrons II (PHAZE II) sounding rocket was launched in February 1997 into active pre-midnight aurora. The resulting high frequency wave data are dominated by Langmuir waves. Consistent with many previous observations the Langmuir waves are sporadic, occurring in bursts lasting up to a few hundred ms. We compute statistics of the electric field amplitudes of these Langmuir waves, with two results. First, the shape of the distribution of running averages of the electric field amplitudes remains approximately stationary for a large range of widths of running average less than ~0.3 ms and for a large range of widths exceeding about 1 ms. The interpretation of this transition timescale is unclear but appears unlikely to be of instrumental origin. Second, for 2.6-ms running averages, corresponding to the latter range, the distribution of the logarithm of electric field amplitudes matches a Gaussian form very well for all nine cases studied in detail, hence the statistics are lognormal. These distributions are consistent with stochastic growth theory (SGT)
Statistics of auroral Langmuir waves
The Physics of Auroral Zone Electrons II (PHAZE II) sounding rocket was launched in February 1997 into active pre-midnight aurora. The resulting high frequency wave data are dominated by Langmuir waves. Consistent with many previous observations the Langmuir waves are sporadic, occurring in bursts lasting up to a few hundred ms. We compute statistics of the electric field amplitudes of these Langmuir waves, with two results. First, the shape of the distribution of running averages of the electric field amplitudes remains approximately stationary for a large range of widths of running average less than ~0.3 ms and for a large range of widths exceeding about 1 ms. The interpretation of this transition timescale is unclear but appears unlikely to be of instrumental origin. Second, for 2.6-ms running averages, corresponding to the latter range, the distribution of the logarithm of electric field amplitudes matches a Gaussian form very well for all nine cases studied in detail, hence the statistics are lognormal. These distributions are consistent with stochastic growth theory (SGT)
Results of the post flash-flood disaster investigations in the Transylvanian Depression (Romania) during the last decade (2001–2010)
Flash-flood disasters are very rare in the Transylvanian Depression. In the
last decades just three events were signalled in the study area, all of them
during the last 10 years. The flash floods occurring in the study area during
the last decade had a significant impact on several localities situated at
the Transylvanian Depression border. Based on the post flash-flood
investigation, the present study intends to find out the main characteristics
of the flash floods and the causes that have led to disasters in a region
rarely affected by such kinds of events. Analyzing the hydrological data, it
has been seen that the maximum intensity of the flash floods was observed in
the upper and middle basins. By comparing the unit peak discharges from the
studied region with other specific peak discharges related to the significant
flash floods from Romania, it was noticed that the events from the
Transylvanian Depression have moderate to low intensity. On the other hand,
the results showed that besides high stream power and unexpected character
common to flash floods, the inappropriate flood risk management measures
increased the dimension of the negative effects, leading to tens of lives
lost and economical damages of tens of millions of dollars
How do we form romantic bonds?: Investigating the effect of attraction on social cognition
Emotions significantly influence our perceptions and interactions with the environment, yet the impact of our emotional states on judging and responding to others remains underexplored. In this thesis, I examined how (romantic) attraction influences our attention (Part I), how we judge others’ intentions (Part II), and whether mimicking another facilitates bond formation (Part III). In two empirical chapters, I demonstrate that people have a strong attentional bias towards visual attractiveness and a tendency to indicate interest in establishing a romantic connection to attractive others. In the subsequent empirical chapter, I show that men are more likely to judge women they find attractive as more sexually aroused. Crucially, in a real-life dating study, I show that men who are attracted to another are more likely to assume mutual interest. Further, I introduce a framework suggesting that people align their actions and emotional states with others to foster romantic relationships. The final empirical chapter suggests that mimicking the attraction cues of others enhances bond formation. Overall, this dissertation sheds light on how attractiveness and attraction affect our attention, our social cognition, and the synchronization of actions and emotions, offering insights into the mechanisms underlying romantic connections.Action Contro
The ontogeny of human laughter
Human adult laughter is characterized by vocal bursts produced predominantly during exhalation, yet apes laugh while exhaling and inhaling. The current study investigated our hypothesis that laughter of human infants changes from laughter similar to that of apes to increasingly resemble that of human adults over early development. We further hypothesized that the more laughter is produced on the exhale, the more positively it is perceived. To test these predictions, novice (n = 102) and expert (phonetician, n = 15) listeners judged the extent to which human infant laughter (n = 44) was produced during inhalation or exhalation, and the extent to which they found the laughs pleasant and contagious. Support was found for both hypotheses, which were further confirmed in two pre-registered replication studies. Likely through social learning and the anatomical development of the vocal production system, infants' initial ape-like laughter transforms into laughter similar to that of adult humans over the course of ontogeny
A combined theoretical and experimental study of the low temperature properties of BaZrO3
Low temperature properties of BaZrO3 are revealed by combining experimental
techniques (X-ray diffraction, neutron scattering and dielectric measurements)
with theoretical first-principles-based methods (total energy and linear
response calculations within density functional theory, and effective
Hamiltonian approaches incorporating/neglecting zero-point phonon vibrations).
Unlike most of the perovskite systems, BaZrO3 does not undergo any
(long-range-order) structural phase transition and thus remains cubic and
paraelectric down to 2 K, even when neglecting zero-point phonon vibrations. On
the other hand, these latter pure quantum effects lead to a negligible thermal
dependency of the cubic lattice parameter below ~ 40 K. They also affect the
dielectricity of BaZrO3 by inducing an overall saturation of the real part of
the dielectric response, for temperatures below ~ 40 K. Two fine structures in
the real part, as well as in the imaginary part, of dielectric response are
further observed around 50-65 K and 15 K, respectively. Microscopic origins
(e.g., unavoidable defects and oxygen octahedra rotation occurring at a local
scale) of such anomalies are suggested. Finally, possible reasons for the facts
that some of these dielectric anomalies have not been previously reported in
the better studied KTaO3 and SrTiO3 incipient ferroelectrics are also
discussed.Comment: 8 pages, 5 figures, submitted to Physical Review
First principles based atomistic modeling of phase stability in PMN-xPT
We have performed molecular dynamics simulations using a shell model
potential developed by fitting first principles results to describe the
behavior of the relaxor-ferroelectric (1-x)PbMg1/3Nb2/3O3-xPbTiO3 (PMN-xPT) as
function of concentration and temperature, using site occupancies within the
random site model. In our simulations, PMN is cubic at all temperatures and
behaves as a polar glass. As a small amount of Ti is added, a weak polar state
develops, but structural disorder dominates, and the symmetry is rhombohedral.
As more Ti is added the ground state is clearly polar and the system is
ferroelectric, but with easy rotation of the polarization direction. In the
high Ti content region, the solid solution adopts ferroelectric behavior
similar to PT, with tetragonal symmetry. The ground state sequence with
increasing Ti content is R-MB-O-MC-T. The high temperature phase is cubic at
all compositions. Our simulations give the slope of the morphotropic phase
boundaries, crucial for high temperature applications. We find that the phase
diagram PMN-xPT can be understood within the random site model.Comment: 27 pages, 9 figure
Poling effect on distribution of quenched random fields in a uniaxial relaxor ferroelectric
The frequency dependence of the dielectric permitivity's maximum has been
studied for poled and unpoled doped relaxor strontium barium niobate
(SBN-61:Cr). In both cases the maximum
found is broad and the frequency dispersion is strong. The present view of
random fields compensation in the unpoled sample is not suitable for explaining
this experimental result. We propose a new mechanism where the dispersion of
quenched random electric fields, affecting the nanodomains, is minimized after
poling. We test our proposal by numerical simulations on a random field Ising
model. Results obtained are in agreement with the polarization's measurements
presented by Granzow et al. [Phys. Rev. Lett {\bf 92}, 065701 (2004)].Comment: 7 pages, 4 figure
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