895 research outputs found
Synchronization problems for unidirectional feedback coupled nonlinear systems
In this paper we consider three different synchronization problems consisting
in designing a nonlinear feedback unidirectional coupling term for two
(possibly chaotic) dynamical systems in order to drive the trajectories of one
of them, the slave system, to a reference trajectory or to a prescribed
neighborhood of the reference trajectory of the second dynamical system: the
master system. If the slave system is chaotic then synchronization can be
viewed as the control of chaos; namely the coupling term allows to suppress the
chaotic motion by driving the chaotic system to a prescribed reference
trajectory. Assuming that the entire vector field representing the velocity of
the state can be modified, three different methods to define the nonlinear
feedback synchronizing controller are proposed: one for each of the treated
problems. These methods are based on results from the small parameter
perturbation theory of autonomous systems having a limit cycle, from nonsmooth
analysis and from the singular perturbation theory respectively. Simulations to
illustrate the effectiveness of the obtained results are also presented.Comment: To appear in Dyn. Contin. Discrete Impuls. Syst., Ser. A, Math. Ana
Some computations on the characteristic variety of a line arrangement
We find monodromy formulas for line arrangements which are fibered with
respect to the projection from one point. We use them to find -dimensional
translated components in the first characteristic variety of the arrangement
determined by a regular -polygon and its diagonals.Comment: 17 pages, 4 figure
Small ruminant Gongylonema pulchrum infection in the South West Algerian desert: prevalence of a sporadic zoonosis
Individual faecal samples were randomly collected from the rectum of goats (n = 120) and sheep (n = 182)
bred in four distinct areas of the South West Algerian desert. All the samples were examined by faecal
flotation technique. A range of gastro-intestinal parasites was recorded by microscopic examination. Special
reference was given to potentially zoonotic nematodes. Typical G. pulchrum eggs were detected as mixed or
single infections in 9.3% of the animals (15% of goats and 5.5% of sheep). Goats were statistically (OR=3.04
[1.35-6.83]) more likely to harbor G. pulchrum infections than sheep. Animals older than 1 year of age were
more likely to be infected with G. pulchrum than younger ones, but these differences di not reach statistically
significant values. Monitoring human infections represents an imperative need of modern society. Anyone
working with sheep and goats or sharing the same environment with them and physicians should be aware of
gongylonemiasis and other potentially zoonotic nematode infections due to ovicaprines, though considered not
life-threatening, sporadic or neglected
Monitoring alkylphenols in water using the polar organic chemical integrative sampler (POCIS): determining sampling rates via the extraction of PES membranes and Oasis beads
Polar organic chemical integrative samplers (POCIS) have previously been used to monitor alkylphenol (AP) contamination in water and produced water. However, only the sorbent receiving phase of the POCIS (Oasis beads) is traditionally analyzed, thus limiting the use of POCIS for monitoring a range of APs with varying hydrophobicity. Here a “pharmaceutical” POCIS was calibrated in the laboratory using a static renewal setup for APs (from 2-ethylphenol to 4-n-nonylphenol) with varying hydrophobicity (log Kow between 2.47 and 5.76). The POCIS sampler was calibrated over its 28 day integrative regime and sampling rates (Rs) were determined. Uptake was shown to be a function of AP hydrophobicity where compounds with log Kow < 4 were preferentially accumulated in Oasis beads, and compounds with log Kow > 5 were preferentially accumulated in the PES membranes. A lag phase (over a 24 h period) before uptake in to the PES membranes occurred was evident. This work demonstrates that the analysis of both POCIS phases is vital in order to correctly determine environmentally relevant concentrations owing to the fact that for APs with log Kow ≤ 4 uptake, to the PES membranes and the Oasis beads, involves different processes compared to APs with log Kow ≥ 4. The extraction of both the POCIS matrices is thus recommended in order to assess the concentration of hydrophobic APs (log Kow ≥ 4), as well as hydrophilic APs, most effectively. © 2017 Elsevier Lt
A Comparison Between Machine Learning and Functional Geostatistics Approaches for Data-Driven Analyses of Sediment Transport in a Pre-Alpine Stream
The problem of providing data-driven models for sediment transport in a pre-Alpine stream in Italy is addressed. This study is based on a large set of measurements collected from real pebbles, traced along the stream through radio-frequency identification tags after precipitation events. Two classes of data-driven models based on machine learning and functional geostatistics approaches are proposed and evaluated to predict the probability of movement of single pebbles within the stream. The first class built upon gradient-boosting decision trees allows one to estimate the probability of movement of a pebble based on the pebbles' geometrical features, river flow rate, location, and subdomain types. The second class is built upon functional kriging, a recent geostatistical technique that allows one to predict a functional profile-that is, the movement probability of a pebble, as a function of the pebbles' geometrical features or the stream's flow rate-at unsampled locations in the study area. Although grounded in different perspectives, both models aim to account for two main sources of uncertainty, namely, (1) the complexity of a river's morphological structure and (2) the highly nonlinear dependence between probability of movement, pebble size and shape, and the stream's flow rate. The performance of the two methods is extensively compared in terms of classification accuracy. The analyses show that despite the different perspectives, the overall performance is adequate and consistent, which suggests that both approaches can provide modeling frameworks for sediment transport. These data-driven approaches are also compared with physics-based ones that are classically used in the hydrological literature. Finally, the use of the developed models in a bottom-up strategy, which starts with the prediction/classification of a single pebble and then integrates the results into a forecast of the grain-size distribution of mobilized sediments, is discussed
Three-dimensional local anisotropy of velocity fluctuations in the solar wind
We analyse velocity fluctuations in the solar wind at magneto-fluid scales in
two datasets, extracted from Wind data in the period 2005-2015, that are
characterised by strong or weak expansion. Expansion affects measurements of
anisotropy because it breaks axisymmetry around the mean magnetic field.
Indeed, the small-scale three-dimensional local anisotropy of magnetic
fluctuations ({\delta}B) as measured by structure functions (SF_B) is
consistent with tube-like structures for strong expansion. When passing to weak
expansion, structures become ribbon-like because of the flattening of SFB along
one of the two perpendicular directions. The power-law index that is consistent
with a spectral slope -5/3 for strong expansion now becomes closer to -3/2.
This index is also characteristic of velocity fluctuations in the solar wind.
We study velocity fluctuations ({\delta}V) to understand if the anisotropy of
their structure functions (SF_V ) also changes with the strength of expansion
and if the difference with the magnetic spectral index is washed out once
anisotropy is accounted for. We find that SF_V is generally flatter than SF_B.
When expansion passes from strong to weak, a further flattening of the
perpendicular SF_V occurs and the small-scale anisotropy switches from
tube-like to ribbon-like structures. These two types of anisotropy, common to
SF_V and SF_B, are associated to distinct large-scale variance anisotropies of
{\delta}B in the strong- and weak-expansion datasets. We conclude that SF_V
shows anisotropic three-dimensional scaling similar to SF_B, with however
systematic flatter scalings, reflecting the difference between global spectral
slopes.Comment: accepted in MNRA
Magnetic field turbulence in the solar wind at sub-ion scales: in situ observations and numerical simulations
We investigate the transition of the solar wind turbulent cascade from MHD to
sub-ion range by means of a detail comparison between in situ observations and
hybrid numerical simulations. In particular we focus on the properties of the
magnetic field and its component anisotropy in Cluster measurements and hybrid
2D simulations. First, we address the angular distribution of wave-vectors in
the kinetic range between ion and electron scales by studying the variance
anisotropy of the magnetic field components. When taking into account the
single-direction sampling performed by spacecraft in the solar wind, the main
properties of the fluctuations observed in situ are also recovered in our
numerical description. This result confirms that solar wind turbulence in the
sub-ion range is characterized by a quasi-2D gyrotropic distribution of
k-vectors around the mean field. We then consider the magnetic compressibility
associated with the turbulent cascade and its evolution from large-MHD to
sub-ion scales. The ratio of field-aligned to perpendicular fluctuations,
typically low in the MHD inertial range, increases significantly when crossing
ion scales and its value in the sub-ion range is a function of the total plasma
beta only, as expected from theoretical predictions, with higher magnetic
compressibility for higher beta. Moreover, we observe that this increase has a
gradual trend from low to high beta values in the in situ data; this behaviour
is well captured by the numerical simulations. The level of magnetic field
compressibility that is observed in situ and in the simulations is in fairly
good agreement with theoretical predictions, especially at high beta,
suggesting that in the kinetic range explored the turbulence is supported by
low-frequency and highly-oblique fluctuations in pressure balance, like kinetic
Alfv\'en waves or other slowly evolving coherent structures.Comment: Manuscript submitted to Frontiers Astronomy and Space Sciences,
Research Topic: Improving the Understanding of Kinetic Processes in Solar
Wind and Magnetosphere: From CLUSTER to MM
Comparative analysis of eliciting capacity of raw and roasted peanuts: the role of gastrointestinal digestion
This study investigated the simultaneous impact of food matrix and processing on the food allergy eliciting capacity of peanuts in a physiologically relevant context. Whole raw and roasted peanuts were subjected to in vitro digestion combining the harmonized oral-gastric-duodenal digestion models with brush border membrane enzymes (BBM) to simulate the jejunal degradation of peptides. SDS-PAGE and HPLC analysis showed that roasting increased digestibility of peanuts and this trend was even more evident after BBM degradation. The eliciting properties of raw and roasted peanuts were assessed by Rat Basophil Leukemia assay in the presence of sera from peanut-allergic patients. As general features, the BBM digestion reduced allergenicity of roasted peanuts compared to the raw counterpart, suggesting that intestinal peptidases effectively contribute to further destroy specific domains of peanut allergens. These findings provide new and more realistic insights in the stability of peanut allergens within their natural matrix
Incentive or Habit Learning in Amphibians?
Toads (Rhinella arenarum) received training with a novel incentive procedure involving access to solutions of different NaCl concentrations. In Experiment 1, instrumental behavior and weight variation data confirmed that such solutions yield incentive values ranging from appetitive (deionized water, DW, leading to weight gain), to neutral (300 mM slightly hypertonic solution, leading to no net weight gain or loss), and aversive (800 mM highly hypertonic solution leading to weight loss). In Experiment 2, a downshift from DW to a 300 mM solution or an upshift from a 300 mM solution to DW led to a gradual adjustment in instrumental behavior. In Experiment 3, extinction was similar after acquisition with access to only DW or with a random mixture of DW and 300 mM. In Experiment 4, a downshift from DW to 225, 212, or 200 mM solutions led again to gradual adjustments. These findings add to a growing body of comparative evidence suggesting that amphibians adjust to incentive shifts on the basis of habit formation and reorganization
Pleistocene soil development and paleoenvironmental dynamics in East Africa: a multidisciplinary study of the Homo-bearing Aalat succession, Dandiero Basin
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