Automated detection of low-dimensional EEG alpha-episodes. An example of application to psychopharmacological data

This paper addresses the practical problems raised by the fact that correlation integrals computed from electroencephalographic signals do not scale. An automated procedure is described for alpha-waves, which is based on the known method of determining the correlation dimension from scaled structures that appear in diagrams of slope-curves. Automation, which is achieved using a moving window that detects the minima of slope-curves, and the density of minima makes it possible to vary the numerous parameters, and to implement tests. The potentialities of the automatic procedure are illustrated by results of psychopharmacological interest, based on the analysis of 22x10(3) alpha-signals, and the computation of 32x10(6) correlation integrals. Previous results concerning the existence of low-dimensional alpha-episodes, lasting in general not more than 5-6 s, are confirmed. Opposing effects upon the correlation dimension are described, at their pharmacological peak, for a dopaminergic agonist (apomorphine) and an atypical antipsychotic, a sigma-receptor ligand. The results also confirm that time reparametrization is a vital check in searches of low-dimensional attractor-ruled dynamics, and they suggest that subjects exhibiting 'high-alpha', i.e. whose alpha-waves are of amplitude A>30 microV, be selected for such investigations.     

Estimation of low bacterial concentration: Listeria monocytogenes in raw milk

A time-series bacteriological analysis has been carried out on milk collected on farms from 1997 to 2001 by a plant producing raw milk soft cheese, with the purpose of assessing the time course of the presence/absence of Listeria monocytogenes. A standard data collection procedure was used, in which farms were tested on a monthly or biweekly basis and 2-3 days after the detection of milk tanker contamination. This procedure yielded low figures for contamination frequencies. The average value and the median of the monthly prevalence of farms detected positive for L. monocytogenes were 2.4 and 0%, respectively. A seasonal effect (with peaks in winter) was observed. Between 1997 and 2001, there was no significant decrease of contamination rates, in spite of the efforts on the contaminated farms. Over the last year of the study (from March 2000 to February 2001), a new data collection procedure was implemented that allowed much better detection of sporadic occurrences. Milk samples were collected from the bulk tank of each participating farm just before pick-up, then stored and subsequently analysed whenever the milk tanker was found contaminated. The average value and the median of the monthly prevalence of positive farms were found equal to 7.7 and 0%, respectively (for a mean prevalence of L. monocytogenes in the milk tanker of 3.2%). These results confirm that farm milk contamination is, most often, a sporadic event In addition to this prevalence study, contamination levels were quantified by enumerating L. monocytogenes using direct plating of small volumes of farm milk previously tested positive. Most often, these levels were extremely low. A simple simulation model shows that, when milk tankers were found positive, contamination levels in the corresponding bulk-tank milk are themselves very low (typically, below 3 L. monocytogenes per millilitre with most probable concentration 0.1 Colony Forming Unit (CFU)/ml and median ranging from 5.10(-2) to 0.1 CFU/ml). Such low levels are very likely to be due to environmental contamination.     

Solvent effect on the conformation in solution of two polyimides

The dilute solution properties of two polyimides have been studied using size exclusion chromatography, light scattering and viscometry in various solvents. Molecular parameters (conformation and aggregation) are found to be solvent dependent. Addition of a non-solvent (H₂O) to 6FDA-mPDA, a fluorine-containing polyimide, or Ultem a polyetherimide, in the good solvent N-methyl-2-pyrrolidone is responsible for an increase in molecular weight. This is attributed to aggregation of polyimides in these conditions. ©1997 SCI     

Effect of extraction conditions on the antioxidant and antiglycation capacity of carbohydrates from Opuntia robusta cladodes

The extraction and characterisation of six crude polysaccharides from Opuntia robusta cladodes, as well as the assessment of their antioxidant and antiglycation activities in vitro, were examined. In this work, carbohydrates were extracted from defatted cladode's peels and pulps through a sequential extraction method in different aqueous medium (neutral, basic and chelating). The obtained polysaccharides were compared in terms of yield and physicochemical properties. Water‐soluble extracts showed the highest yield, while peel's chelating‐soluble extract gave high galacturonic acid content. Preliminary antioxidant in vitro tests suggested that peel's chelating‐soluble extract presented the highest scavenging activity towards DPPH free radicals and inhibition of linoleic acid peroxidation. Furthermore, all extracted polysaccharides showed good potential in inhibiting the nonenzymatic glycation reaction, particularly on the first 3 days of incubation. The obtained results suggested that Opuntia robusta extracts could be explored as natural antioxidant, especially those extracted with chelating agent.     

New semi-IPN scaffolds based on HEMA and collagen modified with itaconic anhydride

Porous semi-IPN scaffolds were synthesized via free radical copolymerization of collagen modified with itaconic anhydride and 2-hydroxyethyl methacrylate, using ammonium persulfate and N,N,N′,N′-tetramethylethylenediamine as redox initiator system, with the aim of overcoming the high enzymatic degradation rate of native collagen scaffolds. The chemical modification of collagen was confirmed by ¹H NMR and FT-IR spectroscopy. The physico-chemical properties of the resulted matrices were investigated by elemental analysis, SEM, enzymatic degradation and water retention studies. The synthesized scaffolds, obtained through an innovative process, have fine microstructures, controlled water retention degree and enhanced stability against enzymatic digestion compared to native collagen. This may broaden the use of collagen-based scaffolds in tissue engineering, particularly for wound dressings.     

Review--Persistence of Listeria monocytogenes in food industry equipment and premises

To understand why Listeria monocytogenes may persist in food industry equipment and premises, notably at low temperature, scientific studies have so far focused on adhesion potential, biofilm forming ability, resistance to desiccation, acid and heat, tolerance to increased sublethal concentration of disinfectants or resistance to lethal concentrations. Evidence from studies in processing plants shows that the factors associated with the presence of L. monocytogenes are those that favor growth. Interestingly, most conditions promoting bacterial growth were shown, in laboratory assays, to decrease adhesion of L. monocytogenes cells. Good growth conditions can be found in so-called harborage sites, i.e. shelters due to unhygienic design of equipment and premises or unhygienic or damaged materials. These sites are hard to eliminate. A conceptual model of persistence/no persistence based on the relative weight of growth vs. outcome of cleaning and disinfection is suggested. It shows that a minimum initial bacterial load is necessary for bacteria to persist in a harborage site and that when a low initial bacterial charge is applied, early cleaning and disinfection is the only way to avoid persistence. We conclude by proposing that there are no strains of L. monocytogenes with unique properties that lead to persistence, but harborage sites in food industry premises and equipment where L. monocytogenes can persist.     

Amphiphilic polysaccharides. Evidence for a competition between intra and intermolecular associations in dilute system

Amphiphilic carboxymethylpullulans differing in their degree of octyl-bearing groups were investigated in dilute solution. Viscometry, flow field-flow fractionation with on-line coupling multi-angle laser light scattering (F4/MALLS) were used to examine conformations and aggregation states in dilute solutions. Polymer/polymer interactions tendency increases with grafting degree. At lower grafting degree, the main species in solution are composed of isolated chains, the conformation of which is close to the precursor. For greater grafting degree, strongly compact structure has been evidenced due to strong intramolecular hydrophobic associations. The transition between dilute and semi-dilute cannot be described by a classical overlapping of chains. The critical concentration (C_cr) appears to be largely function of the content of C₈ groups and presents a minimum for about 20% of octyl groups: at this critical content aggregation trend is found maximum.     

Quantitative risk assessment of human listeriosis from consumption of soft cheese made from raw milk

Microbial hazards have been identified in soft cheese made from raw milk. Quantification of the resulting risk for public health was attempted within the frame of the Codex Alimentarius Commission, 1995 approach to quantitative risk assessment, using Monte Carlo simulation software. Quantitative data could only be found for Listeria monocytogenes. The complete process of cheese making was modeled, from milking to consumption. Using data published on the different sources of milk contamination (environment and mastitis) and bacterial growth, distributions were assumed for parameters of the model. Equations of Farber, J.M., Ross, W.H., Harwing, J. (1996) for general and at-risk populations were used to link the ingested dose of L. monocytogenes to the occurrence of listeriosis. The probability of milk contamination was estimated to be 67% with concentration ranging from 0 to 33 CFU ml-1. The percentage of cheese with a predicted concentration of L. monocytogenes greater than 100 CFU g-1 was low (1.4%). The probability of consuming a contaminated cheese serving was 65.3%. Individual annual cumulative risk of listeriosis, in a population each consuming 50 servings of 31 g, ranged from 1.97 x 10(-9) to 6.4 x 10(-8) in a low-risk sub-population and 1.04 10(-6) to 7.19 10(-5) in a high-risk sub-population. The average number of expected cases of listeriosis per year was 57 for a high-risk sub-population and one for a low-risk healthy sub-population. When the frequency of environmental milk contamination was reduced in the model and L. monocytogenes mastitis was eliminated, the expected incidence of listeriosis decreased substantially; the average number of expected cases was reduced by a factor of 5. Thus the usefulness of simulation to demonstrate the efficiency of various management options could be demonstrated, even if results should be interpreted with care (as many assumptions had to be made on data and their distributions.     

Latencies in fMRI time-series: effect of slice acquisition order and perception

In BOLD fMRI a detailed analysis of the MRI signal time course sometimes shows time differences between different activated regions. Some researchers have suggested that these latencies could be used to infer the temporal order of activation of these cortical regions. Several effects must be considered, however, before interpreting these latencies. The effect of a slice-dependent time shift (SDTS) with multi-slice acquisitions, for instance, may be important for regions located on different slices. After correction for this SDTS effect the time dispersion between activated regions is significantly decreased and the correlation between the MRI signal time course and the stimulation paradigm is improved. Another effect to consider is the latency which may exist between perception and stimulus presentation. It is shown that the control of perception can be achieved using a finger-spanning technique during the fMRI acquisition. The use of this perception profile rather than an arbitrary waveform derived from the paradigm proves to be a powerful alternative to fMRI data processing, especially with chemical senses studies, when return to baseline is not always correlated to stimulus suppression. This approach should also be relevant to other kinds of stimulation tasks, as a realistic way of monitoring the actual task performance, which may depend on attention, adaptation, fatigue or even variability of stimulus presentation.