1,031 research outputs found
Classes of random walks on temporal networks with competing timescales
Random walks find applications in many areas of science and are the heart of
essential network analytic tools. When defined on temporal networks, even basic
random walk models may exhibit a rich spectrum of behaviours, due to the
co-existence of different timescales in the system. Here, we introduce random
walks on general stochastic temporal networks allowing for lasting
interactions, with up to three competing timescales. We then compare the mean
resting time and stationary state of different models. We also discuss the
accuracy of the mathematical analysis depending on the random walk model and
the structure of the underlying network, and pay particular attention to the
emergence of non-Markovian behaviour, even when all dynamical entities are
governed by memoryless distributions.Comment: 16 pages, 5 figure
Random walk on temporal networks with lasting edges
We consider random walks on dynamical networks where edges appear and
disappear during finite time intervals. The process is grounded on three
independent stochastic processes determining the walker's waiting-time, the
up-time and down-time of edges activation. We first propose a comprehensive
analytical and numerical treatment on directed acyclic graphs. Once cycles are
allowed in the network, non-Markovian trajectories may emerge, remarkably even
if the walker and the evolution of the network edges are governed by memoryless
Poisson processes. We then introduce a general analytical framework to
characterize such non-Markovian walks and validate our findings with numerical
simulations.Comment: 18 pages, 18 figure
Nonparametric regression analysis of uncertain and imprecise data using belief functions
AbstractThis paper introduces a new approach to regression analysis based on a fuzzy extension of belief function theory. For a given input vector x, the method provides a prediction regarding the value of the output variable y, in the form of a fuzzy belief assignment (FBA), defined as a collection of fuzzy sets of values with associated masses of belief. The output FBA is computed using a nonparametric, instance-based approach: training samples in the neighborhood of x are considered as sources of partial information on the response variable; the pieces of evidence are discounted as a function of their distance to x, and pooled using Dempster’s rule of combination. The method can cope with heterogeneous training data, including numbers, intervals, fuzzy numbers, and, more generally, fuzzy belief assignments, a convenient formalism for modeling unreliable and imprecise information provided by experts or multi-sensor systems. The performances of the method are compared to those of standard regression techniques using several simulated data sets
Le roi, les légistes et le parlement de Paris aux XIVe et XVe siècles : contradictions dans la perception du pouvoir de « faire loy » ?
Avant Bodin au XVIe siècle, les juristes médiévaux inspirés par le droit romano-canonique ont fait de la loi un instrument privilégié de la puissance du prince. Le pouvoir de condere legem est reconnu au roi de France dès la fin du XIIe siècle par les canonistes favorables à l’émergence de royaumes indépendants face à un pouvoir impérial déclinant. Le roi devenu lex animata, se voit attribuer la faculté de dare, solvere, condere leges par le droit romano-canonique, véhicule de l’exaltation d’..
In vivo neurochemical measurements in cerebral tissues using a droplet-based monitoring system.
Direct collection of extracellular fluid (ECF) plays a central role in the monitoring of neurological disorders. Current approaches using microdialysis catheters are however drastically limited in term of temporal resolution. Here we show a functional in vivo validation of a droplet collection system included at the tip of a neural probe. The system comprises an advanced droplet formation mechanism which enables the collection of neurochemicals present in the brain ECF at high-temporal resolution. The probe was implanted in a rat brain and could successfully collect fluid samples organized in a train of droplets. A microfabricated target plate compatible with most of the surface-based detection methods was specifically developed for sample analysis. The time-resolved brain-fluid samples are analyzed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results provide a time evolution picture of the cerebral tissues neurochemical composition for selected elements known for their involvement in neurodegenerative diseases
Central venous O2 saturation and venous-to-arterial CO2 difference as complementary tools for goal-directed therapy during high-risk surgery
International audienceIntroduction: Central venous oxygen saturation (ScvO 2) is a useful therapeutic target in septic shock and high-risk surgery. We tested the hypothesis that central venous-to-arterial carbon dioxide difference (P(cv-a)CO 2), a global index of tissue perfusion, could be used as a complementary tool to ScvO 2 for goal-directed fluid therapy (GDT) to identify persistent low flow after optimization of preload has been achieved by fluid loading during high-risk surgery. Methods: This is a secondary analysis of results obtained in a study involving 70 adult patients (ASA I to III), undergoing major abdominal surgery, and treated with an individualized goal-directed fluid replacement therapy. All patients were managed to maintain a respiratory variation in peak aortic flow velocity below 13%. Cardiac index (CI), oxygen delivery index (DO 2 i), ScvO 2 , P(cv-a)CO 2 and postoperative complications were recorded blindly for all patients. Results: A total of 34% of patients developed postoperative complications. At baseline, there was no difference in demographic or haemodynamic variables between patients who developed complications and those who did not. In patients with complications, during surgery, both mean ScvO 2 (78 ± 4 versus 81 ± 4%, P = 0.017) and minimal ScvO 2 (minScvO 2) (67 ± 6 versus 72 ± 6%, P = 0.0017) were lower than in patients without complications, despite perfusion of similar volumes of fluids and comparable CI and DO 2 i values. The optimal ScvO 2 cutoff value was 70.6% and minScvO 2 < 70% was independently associated with the development of postoperative complications (OR = 4.2 (95% CI: 1.1 to 14.4), P = 0.025). P(cv-a)CO 2 was larger in patients with complications (7.8 ± 2 versus 5.6 ± 2 mmHg, P < 10-6). In patients with complications and ScvO 2 ≥71%, P(cv-a)CO 2 was also significantly larger (7.7 ± 2 versus 5.5 ± 2 mmHg, P < 10-6) than in patients without complications. The area under the receiver operating characteristic (ROC) curve was 0.785 (95% CI: 0.74 to 0.83) for discrimination of patients with ScvO 2 ≥71% who did and did not develop complications, with 5 mmHg as the most predictive threshold value
Endocarditis in Cattle Caused by Bartonella bovis
This study aimed to determine the role of Bartonella as an endocarditis agent in cattle. Bartonella bovis was identified by PCR, gene sequences analysis, and specific internal transcribed spacer amplicon product size in 2 bovine endocarditis cases with high antibody titers, which demonstrates that B. bovis is a pathogen for cattle
Simulations of the grand design galaxy M51: a case study for analysing tidally induced spiral structure
We present hydrodynamical models of the grand design spiral M51 (NGC 5194),
and its interaction with its companion NGC 5195. Despite the simplicity of our
models, our simulations capture the present day spiral structure of M51
remarkably well, and even reproduce details such as a kink along one spiral
arm, and spiral arm bifurcations. We investigate the offset between the stellar
and gaseous spiral arms, and find at most times (including the present day)
there is no offset between the stars and gas to within our error bars. We also
compare our simulations with recent observational analysis of M51. We compute
the pattern speed versus radius, and like the observations, find no single
global pattern speed. We also show that the spiral arms cannot be fitted well
by logarithmic spirals. We interpret these findings as evidence that M51 does
not exhibit a quasi-steady density wave, as would be predicted by density wave
theory. The internal structure of M51 derives from the complicated and
dynamical interaction with its companion, resulting in spiral arms showing
considerable structure in the form of short-lived kinks and bifurcations.
Rather than trying to model such galaxies in terms of global spiral modes with
fixed pattern speeds, it is more realistic to start from a picture in which the
spiral arms, while not being simple material arms, are the result of tidally
induced kinematic density `waves' or density patterns, which wind up slowly
over time.Comment: 23 pages, 20 figures, accepted for publication in MNRA
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