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.     

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.     

Nested Quantum Search and NP-Hard Problems

A quantum algorithm is known that solves an unstructured search problem in a number of iterations of order , where d is the dimension of the search space, whereas any classical algorithm necessarily scales as O(d). It is shown here that an improved quantum search algorithm can be devised that exploits the structure of a tree search problem by nesting this standard search algorithm. The number of iterations required to find the solution of an average instance of a constraint satisfaction problem scales as , with a constant α < 1 depending on the nesting depth and the problem considered. When applying a single nesting level to a problem with constraints of size 2 such as the graph coloring problem, this constant α is estimated to be around 0.62 for average instances of maximum difficulty. This corresponds to a square-root speedup over a classical nested search algorithm, of which our presented algorithm is the quantum counterpart. Received: August 17, 1998; revised version: December 1, 1999     

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.     

Entanglement May Enhance Channel Capacity in Arbitrary Dimensions

We consider explicitly two examples of d-dimensional quantum channels with correlated noise and show that, in agreement with previous results on Pauli qubit channels, there are situations where maximally entangled input states achieve higher values of the output mutual information than product states. We obtain a strong dependence of this effect on the nature of the noise correlations as well as on the parity of the space dimension, and conjecture that when entanglement gives an advantage in terms of mutual information, maximally entangled states achieve the channel capacity.     

Analysis of arabic gum: Study of degradation and water desorption processes

Arabic gum is very much used in the agroalimentary industry, mainly as an emulsifier. It is a natural origin polysaccharide and therefore subject to more or less important variabilities of its properties. This work deals with two similar polysaccharides exuded by Acacia senegal of different history and an Acacia seyal sample. To characterize these samples, wide angle X-ray scattering (WAXS) and thermogravimetric analysis in dynamic and isothermal mode are used.The initial structure checked by X-ray diffraction allows to affirm that samples are equivalent in their crystalline structure. The activation energy used to characterize the main degradation process is the same for A. senegal samples, but higher for the A. seyal gum sample. Differences are furthermore observed for the kinetics of water desorption. We conclude that the samples from the same type of gum (A. senegal) are very similar and that A. seyal exudates can be detected by this technique. The water desorption of the two exudates is different.     

Hydrogels Based on Pullulan Crosslinked with sodium trimetaphosphate (STMP): Rheological study

Summary Hydrogels from pullulan crosslinked with sodium trimetaphosphate (STMP) under alkaline condition have been investigated by rheological measurements. The influence of reagents concentration (pullulan, STMP, NaOH) on kinetics of reaction and rheological properties is reported. Increasing concentrations of any reagents lead to an increase of the crosslinking kinetics. Increasing the polymer concentration leads to a stronger gel whereas an increase of crosslinking reagent (STMP) evidences a critical concentration above which the rheological properties of the gel do not change anymore. This may be explained by the specificity of the system for which the polymer concentration is high and negative charges appear.     

Single DNA molecule patterning for high-throughput epigenetic mapping

We present a method for profiling the 5-methyl cytosine distribution on single DNA molecules. Our method combines soft-lithography and molecular elongation to form ordered arrays estimated to contain more than 250 000 individual DNA molecules immobilized on a solid substrate. The methylation state of the DNA is detected and mapped by binding of fluorescently labeled methyl-CpG binding domain peptides to the elongated dsDNA molecules and imaging of their distribution. The stretched molecules are fixed in their extended configuration by adsorption onto the substrate so analysis can be performed with high spatial resolution and signal averaging. We further prove this technique allows imaging of DNA molecules with different methylation states.     

A Protocol for Packet Network Intercommunication

A protocol that supports the sharing of resources that exist in different packet switching networks is presented. The protocol provides for variation in individual network packet sizes, transmission failures, sequencing, flow control, end-to-end error checking, and the creation and destruction of logical process-to-process connections. Some implementation issues are considered, and problems such as internetwork routing, accounting, and timeouts are exposed.     

Cloning a qutrit

Several classes of state-dependent quantum cloners for three-level systems are investigated. These cloners optimally duplicate some of the four maximally-conjugate bases with an equal fidelity, thereby extending the phasecovariant qubit cloner to qutrits. Three distinct classes of qutrit cloners can be distinguished, depending on whether two, three, or four maximally-conjugate bases are cloned as well (the latter case simply corresponds to the universal qutrit cloner). These results apply to symmetric as well as asymmetric cloners, so that the balance between the fidelity of the two clones can also be analysed.