348 research outputs found
Inertial- and Dissipation-Range Asymptotics in Fluid Turbulence
We propose and verify a wave-vector-space version of generalized extended
self similarity and broaden its applicability to uncover intriguing, universal
scaling in the far dissipation range by computing high-order (\leq 20\/)
structure functions numerically for: (1) the three-dimensional, incompressible
Navier Stokes equation (with and without hyperviscosity); and (2) the GOY shell
model for turbulence. Also, in case (2), with Taylor-microscale Reynolds
numbers 4 \times 10^{4} \leq Re_{\lambda} \leq 3 \times 10^{6}\/, we find
that the inertial-range exponents (\zeta_{p}\/) of the order - p\/
structure functions do not approach their Kolmogorov value p/3\/ as
Re_{\lambda}\/ increases.Comment: RevTeX file, with six postscript figures. epsf.tex macro is used for
figure insertion. Packaged using the 'uufiles' utilit
Clinical use of various endovascular stenting techniques in challenging coronary interventions
Aim. Development of an algorithm of actions for stenting of artery stenosis during challenging percutaneous coronary interventions (PCI) based on the analysis of the results of different endovascular techniques.
Methods. We analyzed the experience of the department of radiologic endovascular diagnosis and treatment of Stavropol regional clinical hospital for endovascular surgical treatment of atherosclerosis of coronary arteries. The study included 317 cases of coronary interventions with technically impossible stent delivery to stenosis by standard method along the front-line guidewire and standard choice of the guide in case of distal TIMI 3 flow. For the study the patients were divided into 3 groups comparable by the number of subjects: 104, 113 and 100 respectively. For each group we determined different stages of enhancing support with consistent step-wise transition. The groups differed by the used methods of enhancing support and consistency of their use. Among other methods of support group 2 included the method of guide change and delivery of the second guidewire of enhanced support. At the same time groups 1 and 3 used these methods separately.
Results. The smallest number of unsuccessful interventions was observed in group 2 compared to those of groups 1 and 3. The relative risk indicators also demonstrate the high effectiveness of tactics used in the group 2.
Conclusion. The most preferable method for the necessary support when stent delivery distal to stenosis is impossible, is a choice of optimal guide and use of the second guidewire of enhanced support
Turbulence and Multiscaling in the Randomly Forced Navier Stokes Equation
We present an extensive pseudospectral study of the randomly forced
Navier-Stokes equation (RFNSE) stirred by a stochastic force with zero mean and
a variance , where is the wavevector and the dimension . We present the first evidence for multiscaling of velocity structure
functions in this model for . We extract the multiscaling exponent
ratios by using extended self similarity (ESS), examine their
dependence on , and show that, if , they are in agreement with those
obtained for the deterministically forced Navier-Stokes equation (NSE). We
also show that well-defined vortex filaments, which appear clearly in studies
of the NSE, are absent in the RFNSE.Comment: 4 pages (revtex), 6 figures (postscript
Universal statistics of non-linear energy transfer in turbulent models
A class of shell models for turbulent energy transfer at varying the
inter-shell separation, , is investigated. Intermittent corrections in
the continuous limit of infinitely close shells () have
been measured. Although the model becomes, in this limit, non-intermittent, we
found universal aspects of the velocity statistics which can be interpreted in
the framework of log-poisson distributions, as proposed by She and Waymire
(1995, Phys. Rev. Lett. 74, 262). We suggest that non-universal aspects of
intermittency can be adsorbed in the parameters describing statistics and
properties of the most singular structure. On the other hand, universal aspects
can be found by looking at corrections to the monofractal scaling of the most
singular structure. Connections with similar results reported in other shell
models investigations and in real turbulent flows are discussed.Comment: 4 pages, 2 figures available upon request to [email protected]
Dragon-kings: mechanisms, statistical methods and empirical evidence
This introductory article presents the special Discussion and Debate volume
"From black swans to dragon-kings, is there life beyond power laws?" published
in Eur. Phys. J. Special Topics in May 2012. We summarize and put in
perspective the contributions into three main themes: (i) mechanisms for
dragon-kings, (ii) detection of dragon-kings and statistical tests and (iii)
empirical evidence in a large variety of natural and social systems. Overall,
we are pleased to witness significant advances both in the introduction and
clarification of underlying mechanisms and in the development of novel
efficient tests that demonstrate clear evidence for the presence of
dragon-kings in many systems. However, this positive view should be balanced by
the fact that this remains a very delicate and difficult field, if only due to
the scarcity of data as well as the extraordinary important implications with
respect to hazard assessment, risk control and predictability.Comment: 20 page
Acoustic radiation controls friction: Evidence from a spring-block experiment
Brittle failures of materials and earthquakes generate acoustic/seismic waves
which lead to radiation damping feedbacks that should be introduced in the
dynamical equations of crack motion. We present direct experimental evidence of
the importance of this feedback on the acoustic noise spectrum of
well-controlled spring-block sliding experiments performed on a variety of
smooth surfaces. The full noise spectrum is quantitatively explained by a
simple noisy harmonic oscillator equation with a radiation damping force
proportional to the derivative of the acceleration, added to a standard viscous
term.Comment: 4 pages including 3 figures. Replaced with version accepted in PR
Моделирование парожидкостного равновесия в системе: α,γ-дихлоргидрин глицерина– α-монохлоргидрин глицерина–глицерин– хлористый водород–вода
. Both the experimental LLE and VLE data were compared with the correlated values obtained by means of the NRTL equation. Satisfactory agreement between the calculated values and experimental data was achievedполучена модель парожидкостного равновесия для пятикомпонентной промышленной системы α,γ-дихлоргидрин глицерина–α-монохлоргидрин глицерина–глицерин–хлористый водород–вода
Heavy-Tailed Distribution of Cyber-Risks
With the development of the Internet, new kinds of massive epidemics,
distributed attacks, virtual conflicts and criminality have emerged. We present
a study of some striking statistical properties of cyber-risks that quantify
the distribution and time evolution of information risks on the Internet, to
understand their mechanisms, and create opportunities to mitigate, control,
predict and insure them at a global scale. First, we report an exceptionnaly
stable power-law tail distribution of personal identity losses per event, , with . This result is
robust against a surprising strong non-stationary growth of ID losses
culminating in July 2006 followed by a more stationary phase. Moreover, this
distribution is identical for different types and sizes of targeted
organizations. Since , the cumulative number of all losses over all events
up to time increases faster-than-linear with time according to
, suggesting that privacy, characterized by personal
identities, is necessarily becoming more and more insecure. We also show the
existence of a size effect, such that the largest possible ID losses per event
grow faster-than-linearly as with the organization size . The
small value of the power law distribution of ID losses is
explained by the interplay between Zipf's law and the size effect. We also
infer that compromised entities exhibit basically the same probability to incur
a small or large loss.Comment: 9 pages, 3 figure
Autoregressive modeling of transfer functions in frequency domain to determine complex travel times
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