Rodlike Complexes of a Polyelectrolyte (Hyaluronan) and a Protein (Lysozyme) observed by SANS

We study by Small Angle Neutron Scattering (SANS) the structure of Hyaluronan -Lysozyme complexes. Hyaluronan (HA) is a polysaccharide of 9 nm intrinsic persistence length that bears one negative charge per disaccharide monomer (Mmol = 401.3 g/mol); two molecular weights, Mw = 6000 and 500 000 Da were used. The pH was adjusted at 4.7 and 7.4 so that lysozyme has a global charge of +10 and + 8 respectively. The lysozyme concentration was varied from 3 to 40 g/L, at constant HA concentration (10 g/L). At low protein concentration, samples are monophasic and SANS experiments reveal only fluctuations of concentration although, at high protein concentration, clusters are observed by SANS in the dense phase of the diphasic samples. In between, close to the onset of the phase separation, a distinct original scattering is observed. It is characteristic of a rod-like shape, which could characterize "single" complexes involving one or a few polymer chains. For the large molecular weight (500 000) the rodlike rigid domains extend to much larger length scale than the persistence length of the HA chain alone in solution and the range of the SANS investigation. They can be described as a necklace of proteins attached along a backbone of diameter one or a few HA chains. For the short chains (Mw ~ 6000), the rod length of the complexes is close to the chain contour length (~ 15 nm)

Spatial structure and composition of polysaccharide-protein complexes from Small Angle Neutron Scattering

We use Small Angle Neutron Scattering (SANS), with an original analysis method, to obtain both the characteristic sizes and the inner composition of lysozyme-pectin complexes depending on the charge density. Lysozyme is a globular protein and pectin a natural anionic semiflexible polysaccharide with a degree of methylation (DM) 0, 43 and 74. For our experimental conditions (buffer ionic strength I = 2.5 10-2 mol/L and pH between 3 and 7), the electrostatic charge of lysozyme is always positive (from 8 to 17 depending on pH). The pectin charge per elementary chain segment is negative and can be varied from almost zero to one through the change of DM and pH. The weight molar ratio of lysozyme on pectin monomers is kept constant. The ratio of negative charge content per volume to positive charge content per volume, -/+, is varied between 10 and 0.007. On a local scale, for all charged pectins, a correlation peak appears at 0.2 {\AA}-1 due to proteins clustering inside the complexes. On a large scale, the complexes appear as formed of spherical globules with a well defined radius of 10 to 50 nm, containing a few thousands proteins. The volume fraction Phi of organic matter within the globules derived from SANS absolute cross-sections is around 0.1. The protein stacking, which occurs inside the globules, is enhanced when pectin is more charged, due to pH or DM. The linear charge density of the pectin determines the size of the globules for pectin chains of comparable molecular weights whether it is controlled by the pH or the DM. The radius of the globules varies between 10 nm and 50 nm. In conclusion the structure is driven by electrostatic interactions and not by hydrophobic interactions. The molecular weight also has a large influence on the structure of the complexes since long chains tend to form larger globules. This maybe one reason why DM and pH are not completely equivalent in our system since DM 0 has a short mass, but this may not be the only one. For very low pectin charge (-/+ = 0.07), globules do not appear and the scattering signals a gel-like structure. We did not observe any beads-on-a-string structure

Structure Transition in PSS/Lysozyme Complexes: A Chain-Conformation-Driven Process, as Directly Seen by Small Angle Neutron Scattering

Measurements of chain conformation in proteins/polyelectrolytes complexes (lysozyme and PSSNa) show that the crossover observed between an open structure -a chain network crosslinked by the proteins, and a globular one - dense globules of ~ 10 nm aggregated in a fractal way, results from a conformation modification prior to the transition. Before showing this, we have widened the parameters range for the observation of the transition. We had shown before that the two structures can be formed depending on chain length (for a given [PSS]/[lysozyme] ratio): gel for large chains, globules for short chains. We show here that the crossover between these two regimes can also be reached as a function of chains concentration or salinity of the buffer. Since all these crossover parameters act on chains overlapping concentration c*, we reinforce the idea of a transition from the dilute to the semi-dilute regime, but c* is shifted compared to pure PSS solutions. In order to understand this, we have measured by SANS the conformation of a single chain of PSS in presence of proteins within the complexes. This is achieved by a specific labeling trick where we take advantage of the fact that lysozyme and hydrogenated PSS chains have the same neutron scattering length density. In the gel structure, the PSS chains keep a wormlike structure as in pure solutions, but their persistence length is strongly reduced, from 50 {\AA} without proteins to 20 {\AA} in average with lysozyme. With this value of 20 {\AA}, we calculate new overlapping thresholds (concentration, mass, ionic strength) in agreement with observed ones. In a second stage, after the globular structure is formed, the PSS chains get a third conformation, no longer wormlike, but more collapsed, within the globules

Adsorption of MultiLamellar tubes with a temperature tunable diameter at the air-water interface: a process driven by the bulk properties

The behavior at the air/water interface of multilamellar tubes made of the ethanolamine salt of the 12-hydroxy stearic acid as a function of the temperature has been investigated using Neutron Reflectivity. Those tubes are known to exhibit a temperature tunable diameter in the bulk. We have observed multilamellar tubes adsorbed at the air/water interface by specular neutron reflectivity. Interestingly, at the interface, the adsorbed tubes exhibit the same behavior than in the bulk upon heating. There is however a peculiar behavior at around 50\degree for which the increase of the diameter of the tubes at the interface yields an unfolding of those tubes into a multilamellar layer. Upon further heating, the tubes re-fold and their diameter re-decrease after what they melt as observed in the bulk. All structural transitions at the interface are nevertheless shown to be quasi-completely reversible. This provides to the system a high interest for its interfacial properties because the structure at the air/water interface can be tuned easily by the temperature

IMPLEMENTATION OF MOTION ESTIMATION BASED ON HETEROGENEOUS PARALLEL COMPUTING SYSTEM WITH OPENC

International audienceHeterogeneous computing system increases the performance of parallel computing in many domain of general purpose computing with CPU, GPU and other accelerators. Open Computing Language (OpenCL) is the first open, royaltyfree standard for heterogenous computing on multi hardware platforms. In this paper, we propose a parallel Motion Estimation (ME) algorithm implemented using OpenCL and present several optimization strategies applied in our OpenCL implementation of the motion estimation. In the same time, we implement the proposed algorithm on our heterogeneous computing system which contains one CPU and one GPU, and propose one method to determine the balance to distribute the workload in heterogeneous computing system with OpenCL. According to experiments, our motion estimator with achieves 100 to 150 speed-up compared with its implementation with C code executed by single CPU core and our proposed method obtains obviously enhancement of performance in based on our heterogeneous computing system

Advanced list scheduling heuristic for task scheduling with communication contention for parallel embedded systems

WOSInternational audienceModern embedded systems tend to use multiple cores or processors for processing parallel applications. This paper indeed aims at task scheduling with communication contention for parallel embedded systems and proposes three advanced techniques to improve the list scheduling heuristic. Five groups of node levels (two existing groups and three new groups) are firstly used as node priorities to generate node lists. Then the critical child technique improves the selection of a processor in the scheduling process. Finally, the communication delay technique enlarges the idle time intervals on communication links. We also propose an advanced dynamic list scheduling heuristic by combining the three techniques. Experimental results show that the combined advanced dynamic heuristic is efficient to shorten the schedule length for most of the randomly generated DAGs in the cases of medium and high communication. Our method accelerates an application up to 80% in the case of high communication and can also reduce the use of hardware resources

A List Scheduling Heuristic with New Node Priorities and Critical Child Technique for Task Scheduling with Communication Contention

International audienceTask scheduling is an important aspect for parallel programming. In this paper, the program to be scheduled is modeled as a Directed Acyclic Graph (DAG), and we target parallel embedded systems of multiple processors connected by buses and switches. This paper presents improvements for list scheduling heuristics with communication contention. We use new node priorities (top level and bottom level) to sort nodes and use an advanced technique of critical child to select a processor to execute a node. Experimental results show that our method is effective to reduce the schedule length, and the performance is greatly improved in the cases of medium and high communication. Since the communication cost is increasing from medium to high in modern applications like digital communication and video compression, our method will work well for scheduling these applications on parallel embedded systems

A List Scheduling Heuristic with New Node Priorities and Critical Child Technique for Task Scheduling with Communication Contention

International audienceTask scheduling is an important aspect for parallel programming. In this paper, the program to be scheduled is modeled as a Directed Acyclic Graph (DAG), and we target parallel embedded systems of multiple processors connected by buses and switches. This paper presents improvements for list scheduling heuristics with communication contention. We use new node priorities (top level and bottom level) to sort nodes and use an advanced technique of critical child to select a processor to execute a node. Experimental results show that our method is effective to reduce the schedule length, and the performance is greatly improved in the cases of medium and high communication. Since the communication cost is increasing from medium to high in modern applications like digital communication and video compression, our method will work well for scheduling these applications on parallel embedded systems

Heuristique statique améliorée d'ordonnancement de tâches: impact sur le tri des tâches et sur l'allocation de processeur

National audienceL'ordonnancement de tâches est une étape importante dans le prototypage rapide d'applications de traitement d'images sur des systèmes parallèles embarqués. Nous présentons ainsi dans cet article une heuristique statique améliorée d'ordonnancement par liste : d'une part, cette heuristique intègre de nouvelles règles de priorité de tâches, tenant compte de la contention sur les communications entre tâches ; d'autre part, cette heuristique affine l'allocation d'un processeur à une tâche courante, en impactant le choix du processeur par un ordonnancement partiel de la tâche successeur critique (" critical child ") à la tâche courante. Nos résultats expérimentaux soulignent une accélération effective de l'application implantée, dans un contexte de moyenne comme de forte communication