LD12301
Ultrahigh energy photons as a probe of Universe's highest energy particles
The origin of ultrahigh energy cosmic rays (UHECRs) has been one of the biggest mysteries in astrophysics. There are two ways to identify the sources: examining the arrival directions of UHECRs, and hunting neutrinos and photons produced via hadronic interactions between cosmic rays and ambient photons and nucleons. The latter is more crucial when the sources are transient like gamma-ray bursts, because cosmic rays have significant time delays by cosmic magnetic fields while neutrinos and photons may not. In this letter, we have demonstrated that ultrahigh energy (above 10 EeV) photons produced in the source can be the most useful probe of nearby transient UHECR sources. Their detections directly suggest UHECR accelerators, and give us useful information on the uncertain cosmic radio background and cosmic magnetic fields. Furthermore, they may allow us a much more stringent test of possible Lorentz invariance violation that is often predicted in quantum gravity theories. Such ultrahigh energy photons could be detected by the Pierre Auger observatory and future larger detectors such as the planned JEM-EUSO can provide us with more chances to observe them.
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LF12637
HOW VIBRATION REDUCES FRICTION
It is known empirically that friction between two bodies can be
reduced if the system is vibrated, but it turns out that this only
happens under well defined conditions.
Using molecular dynamics simulations of repulsive particles confined
between a horizontally driven top plate and a vertically oscillating
bottom plate, Capozza et al identify the range
of vibration frequencies for which friction is strongly suppressed.
This range depends on the vibrating amplitude, the normal applied
load, the system inertia and the damping constant. The result is
important because it could help improve frictional properties of nano-
devices. In addition, it could be used to explain earthquake
triggering by small dynamic perturbations: vibrations, for certain
frequencies, can induce a drastic reduction of the friction force
between fault planes, leading to an earthquake.
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EB10523
Kramers-Moyal coefficients in the analysis and modeling of heart rate
variability
Modeling of recorded time series may be used as a method of analysis
for heart rate variability studies. In particular, the extraction of
the first two Kramers-Moyal coefficients has been used in this
context. Recently, the method was applied to a wide range of signal
analysis: from financial data to physiological and biological time
series. Modeling of the signal is important for the prediction and
interpretation of the dynamics underlying the process. The method
requires the determination of the Markov time. Obtaining the drift and
diffusion term of the Kramers-Moyal expansion is crucial for the
modeling of the original time series with the Langevin equation. Both
Tabar et al. and T. Kuusela et al. suggested that these terms may be
used to distinguish healthy subjects from those with heart failure.
The research groups applied a somewhat different methodology and
obtained substantially different ranges of the Markov time. We show
that the two studies may be considered consistent with each other as
Kuusela et al. analysed 24 h recordings while Tabar et al. analyzed
daytime and nighttime recordings, separately. However, both groups
suggested using the Langevin equation for modeling of time series
which requires the fluctuation force to be a Gaussian. We analyzed
heart rate variability recordings for ten male young (age 26-4 + 3 y)
healthy subjects. 24 h recordings were analyzed and 6 h long daytime
and nighttime fragments were selected. Similar properties of the data
were observed in all recordings but all the nighttime data and seven
of the ten 24 h series exhibited higher order, non-negligible
Kramers-Moyal coefficients. In such a case, the reconstruction of the
time series using the Langevin equation is impossible. The
non-negligible higher order coefficients are due to autocorrelation in
the data. This effect may be interpreted as a result of a
physiological phenomenon (especially occurring for nighttime data):
respiratory sinus arrhythmia. We detrended the nighttime recordings
for the healthy subjects and obtained an asymmetry in the dependence
of the diffusion term on the rescaled heart rate. This asymmetry seems
to be an effect of different time scales during the inspiration and
the expiration phase of breathing. The asymmetry was significantly
decreased in the diffusion term found for detrended nighttime
recordings obtained from 5 hypertrophic cardiomyopathy (HCM) patients.
We conclude that the effect of RSA is decreased in the heart rate
variability of HCM patients - a result which may contribute to a
better medical diagnosis by supplying a new quantitative measure of
RSA.
