489 research outputs found
The statistical properties of the city transport in Cuernavaca (Mexico) and Random matrix ensembles
We analyze statistical properties of the city bus transport in Cuernavaca
(Mexico) and show that the bus arrivals display probability distributions
conforming those given by the Unitary Ensemble of random matrices.Comment: 4 pages, 3 figure
Probing complex RNA structures by mechanical force
RNA secondary structures of increasing complexity are probed combining single
molecule stretching experiments and stochastic unfolding/refolding simulations.
We find that force-induced unfolding pathways cannot usually be interpretated
by solely invoking successive openings of native helices. Indeed, typical
force-extension responses of complex RNA molecules are largely shaped by
stretching-induced, long-lived intermediates including non-native helices. This
is first shown for a set of generic structural motifs found in larger RNA
structures, and then for Escherichia coli's 1540-base long 16S ribosomal RNA,
which exhibits a surprisingly well-structured and reproducible unfolding
pathway under mechanical stretching. Using out-of-equilibrium stochastic
simulations, we demonstrate that these experimental results reflect the slow
relaxation of RNA structural rearrangements. Hence, micromanipulations of
single RNA molecules probe both their native structures and long-lived
intermediates, so-called "kinetic traps", thereby capturing -at the single
molecular level- the hallmark of RNA folding/unfolding dynamics.Comment: 9 pages, 9 figure
Life events and hemodynamic stress reactivity in the middle-aged and elderly
Recent versions of the reactivity hypothesis, which consider it to be the product of stress exposure and exaggerated haemodynamic reactions to stress that confers cardiovascular disease risk, assume that reactivity is independent of the experience of stressful life events. This assumption was tested in two substantial cohorts, one middle-aged and one elderly. Participants had to indicate from a list of major stressful life events up to six they had experienced in the previous two years. They were also asked to rate how disruptive and stressful they were, at the time of occurrence and now. Blood pressure and pulse rate were measured at rest and in response to acute mental stress. Those who rated the events as highly disruptive at the time of exposure and currently exhibited blunted systolic blood pressure reactions to acute stress. The present results suggest that acute stress reactivity may not be independent of stressful life events experience
Estimating Acceleration and Lane-Changing Dynamics Based on NGSIM Trajectory Data
The NGSIM trajectory data sets provide longitudinal and lateral positional
information for all vehicles in certain spatiotemporal regions. Velocity and
acceleration information cannot be extracted directly since the noise in the
NGSIM positional information is greatly increased by the necessary numerical
differentiations. We propose a smoothing algorithm for positions, velocities
and accelerations that can also be applied near the boundaries. The smoothing
time interval is estimated based on velocity time series and the variance of
the processed acceleration time series. The velocity information obtained in
this way is then applied to calculate the density function of the
two-dimensional distribution of velocity and inverse distance, and the density
of the distribution corresponding to the ``microscopic'' fundamental diagram.
Furthermore, it is used to calculate the distributions of time gaps and
times-to-collision, conditioned to several ranges of velocities and velocity
differences. By simulating virtual stationary detectors we show that the
probability for critical values of the times-to-collision is greatly
underestimated when estimated from single-vehicle data of stationary detectors.
Finally, we investigate the lane-changing process and formulate a quantitative
criterion for the duration of lane changes that is based on the trajectory
density in normalized coordinates. Remarkably, there is a very noisy but
significant velocity advantage in favor of the targeted lane that decreases
immediately before the change due to anticipatory accelerations
Prediction and statistics of pseudoknots in RNA structures using exactly clustered stochastic simulations
Ab initio RNA secondary structure predictions have long dismissed helices
interior to loops, so-called pseudoknots, despite their structural importance.
Here, we report that many pseudoknots can be predicted through long time scales
RNA folding simulations, which follow the stochastic closing and opening of
individual RNA helices. The numerical efficacy of these stochastic simulations
relies on an O(n^2) clustering algorithm which computes time averages over a
continously updated set of n reference structures. Applying this exact
stochastic clustering approach, we typically obtain a 5- to 100-fold simulation
speed-up for RNA sequences up to 400 bases, while the effective acceleration
can be as high as 100,000-fold for short multistable molecules (<150 bases). We
performed extensive folding statistics on random and natural RNA sequences, and
found that pseudoknots are unevenly distributed amongst RNAstructures and
account for up to 30% of base pairs in G+C rich RNA sequences (Online RNA
folding kinetics server including pseudoknots : http://kinefold.u-strasbg.fr/
).Comment: 6 pages, 5 figure
Congested Traffic States in Empirical Observations and Microscopic Simulations
We present data from several German freeways showing different kinds of
congested traffic forming near road inhomogeneities, specifically lane
closings, intersections, or uphill gradients. The states are localized or
extended, homogeneous or oscillating. Combined states are observed as well,
like the coexistence of moving localized clusters and clusters pinned at road
inhomogeneities, or regions of oscillating congested traffic upstream of nearly
homogeneous congested traffic. The experimental findings are consistent with a
recently proposed theoretical phase diagram for traffic near on-ramps [D.
Helbing, A. Hennecke, and M. Treiber, Phys. Rev. Lett. {\bf 82}, 4360 (1999)].
We simulate these situations with a novel continuous microscopic single-lane
model, the ``intelligent driver model'' (IDM), using the empirical boundary
conditions. All observations, including the coexistence of states, are
qualitatively reproduced by describing inhomogeneities with local variations of
one model parameter.
We show that the results of the microscopic model can be understood by
formulating the theoretical phase diagram for bottlenecks in a more general
way. In particular, a local drop of the road capacity induced by parameter
variations has practically the same effect as an on-ramp.Comment: Now published in Phys. Rev. E. Minor changes suggested by a referee
are incorporated; full bibliographic info added. For related work see
http://www.mtreiber.de/ and http://www.helbing.org
Defect Chaos of Oscillating Hexagons in Rotating Convection
Using coupled Ginzburg-Landau equations, the dynamics of hexagonal patterns
with broken chiral symmetry are investigated, as they appear in rotating
non-Boussinesq or surface-tension-driven convection. We find that close to the
secondary Hopf bifurcation to oscillating hexagons the dynamics are well
described by a single complex Ginzburg-Landau equation (CGLE) coupled to the
phases of the hexagonal pattern. At the bandcenter these equations reduce to
the usual CGLE and the system exhibits defect chaos. Away from the bandcenter a
transition to a frozen vortex state is found.Comment: 4 pages, 6 figures. Fig. 3a with lower resolution no
The effects of the spontaneous presence of a spouse/partner and others on cardiovascular reactions to an acute psychological challenge
The presence of supportive others has been associated with attenuated cardiovascular reactivity in the laboratory. The effects of the presence of a spouse and others in a more naturalistic setting have received little attention. Blood pressure and heart rate reactions to mental stress were recorded at home in 1028 married/partnered individuals. For 112 participants, their spouse/partner was present; for 78, at least one other person was present. Women tested with a spouse/partner present showed lower magnitude systolic blood pressure and heart rate reactivity than those tested without. Individuals tested with at least one nonspousal other present also displayed attenuated reactivity. This extends the results of laboratory studies and indicates that the spontaneous presence of others is associated with a reduction in cardiovascular reactivity in an everyday environment; spouse/partner presence would appear to be especially effective for women.\ud
\u
Quantum Magnetization Plateau in Spin-1 Triangular-Lattice Antiferromagnet BaNiSbO
We report the results of magnetization and specific heat measurements on
BaNiSbO, which is a quasi-two-dimensional spin-1 triangular-lattice
antiferromagnet. We observed a nonclassical magnetization plateau at one-third
of the saturation magnetization that is driven by spin frustration and quantum
fluctuation. Exact diagonalization for a 21-site rhombic cluster was performed
to analyze the magnetization process. Experimental and calculated results agree
well.Comment: published in Journal of the Physical Society of Japan 80 (2011)
09370
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