Diffusion of dextran in concentrated solutions

A free-diffusion method has been developed for the determination of the intradiffusion coefficient ('self-diffusion coefficient') of a polymer in highly concentrated solutions. A fraction of the polymer is labelled with a small amount of light-absorbing substituent. The diffusion of this labelled species, present in low concentration, is followed in the presence of a high concentration of unlabelled material with the aid of absorption optics in the analytical ultracentrifuge. The diffusion proceeds over a boundary at which the difference in concentration of unlabelled material is varied. The average concentration of total polymer and the concentration of the labelled material are, however, constant. From theoretical considerations it is shown that by extrapolation of the diffusion coefficient so obtained to zero concentration difference of total material, the intradiffusion coefficient of the polymer at that concentration is obtained. The procedure also permits the ordinary translational diffusion coefficient to be estimated. The method has been applied to two dextran fractions with weight-average molecular weights of 19000 and 150000, which were labelled with fluorescein groups. As expected, the intradiffusion coefficient decreases with increasing polymer concentration, the decrease being more pronounced for the high-molecular-weight material. This decrease in the diffusion rate of dextran is, however, less than the corresponding decrease in the sedimentation rate which proteins with similar hydrodynamic parameters experience in dextran solutions. This agrees with the hypothesis that flexible linear polymers move through a network as chains rather than as hydrodynamic spheres. By combining measurements of the ordinary diffusion coefficient and the intradiffusion coefficient, it is possible to calculate the thermodynamic properties (as expressed by the virial expansion) of the system. This method is of particular importance in studies on concentrated solutions of high-molecular-weight polymers.     

A prototype approach to information system design and development

Many organisations view the development of an information processing system as a linear process consisting of an ordered sequence of steps from conception to hand-over and make no provision for alternative strategies. While excellent in many circumstances, the linear strategy is not the only possible approach. This paper discusses alternatives, with particular reference to a prototype strategy, which has some important advantages.     

A physically-based computer model of aggregate electric waterheating loads

Electric water heaters have been the focus of several previous studies because of their pervasiveness in power systems and their consequent potential importance when considering conservation through more efficient design and operation of the heaters. Also, because such devices are associated with an energy storage capability, they are often considered within load management by direct device control programs. Finally, they tend to be responsible for persistent system load transients in a cold load pickup situation. Understanding of the above issues can be greatly enhanced with the availability of a computer model of aggregate electric water heating loads. A physically-based such model is presented and its dynamic properties are investigated via numerical simulation under various operating conditions and parameter configurations. The results are analyzed in the paper     

Tracking and MAP reconstruction of line scratches in degraded motion pictures

A suitable detection and reconstruction approach is proposed for removing line scratches from degraded motion picture films. The detection procedure consists of two steps. First, a simple 1D-extrema detector provides line scratch candidates. Unlike impulsive distortions, which appear randomly in an image, line artifacts persist across several frames. Furthermore, the detection process is complicated by the fact that lines occur as a natural part in interesting scenes. Therefore, we add a validation step for separating possible line defects from false detections. It consists in tracking the potential line artifacts over the frames using a Kalman filter. A new Bayesian restoration technique, dealing with both low and high frequencies around and inside the detected deteriorations, is investigated to achieve a nearly invisible reconstruction of damaged areas. Accepted: 13 August 2001     

Computing a hyperelliptic integral using arithmetic in the Jacobian of the curve

In this paper, we describe an efficient algorithm for computing an elementary antiderivative of an algebraic function defined on a hyperelliptic curve. Our algorithm combines B. M. Trager's integration algorithm and a technique for computing in the Jacobian of a hyperelliptic curve introduced by D. G. Cantor. Our method has been implemented and successfully compared to Trager's general algorithm.Work partially made at Departement Informatik ETH ZurichUnité de Recherche Associée au CNRS 1586     

Interfacial area and gas-side mass transfer coefficient of a gas—liquid absorption column: pilot-scale comparison of various tray types

The method of gas—liquid absorption with chemical reaction was applied to determine the interfacial area and the gas-side mass transfer coefficient and implemented in a pilot column of diameter 0.45 m. This absorber was equipped successively with different trays of industrial type (bubble-cap, sieve and valve trays), so that a reliable comparison of their respective efficiencies could be made. The influence of weir height was studied especially, and also the effects of gas velocity and liquid load. The experimental results were correlated by means of empirical relations which account for the respective influences of the three parameters and provide a useful basis for extrapolation to industrial absorber design.     

A partition model approach to updating universal scheme interfaces

The updating of relational databases has received extensive attention in the past few years. However, the various methods proposed present two main drawbacks: either the method cannot perform some update because of nondeterminism, or the method is deterministic but leads to counterintuitive results. In this paper, we use partition semantics to study updating in universal scheme interfaces. It is shown that, contrary to other approaches, the main difficulties are due to nondeterminism of deletions. We characterize when a deletion is deterministic or not, and we show how partition semantics allow for choices in certain cases of nondeterminism     

State-feedback control of systems with multiplicative noise via linear matrix inequalities

We consider LTI systems perturbed by parametric uncertainties, modeled as white noise disturbances. We show how to maximize, via state-feedback control, the smallest norm of the noise intensity vector producing instability in the mean square sense, using convex optimization over linear matrix inequalities. We also show how to maximize performance robustness, where performance is measured by expected output energy, with either bounded initial conditions and zero inputs (classical LQG cost), or zero initial conditions and deterministic inputs of bounded energy (a generalization of the H_∞ norm).     

Anorectal reconstruction by coloperineal anastomosis and dynamic double graciloplasty after abdomino-perineal resection

The aim of this study was to assess the technical and functional results of total anorectal reconstruction with double dynamic graciloplasty after abdominoperineal resection (APR). PATIENTS AND METHODS: From May 1995 to December 1996. 10 patients (6 males and 4 females), with a mean age of 54 years (range 39-74), underwent anorectal reconstruction for low rectal adenocarcinoma. All patients had preoperative radiotherapy and six had postoperative chemotherapy. The surgical procedure was performed in three stages: 1) APR, coloperineal anastomosis, double graciloplasty and ileostomy; 2) three months later, implantation of stimulator and leads; 3) after a two-months training period, the stoma was closed. RESULTS: There was no postoperative mortality. Early and late morbidity occurred in 5 patients: 2 colonic fistulas, 1 necrosis of colon, 1 ileostomy prolapse, 1 neosphincter stenosis, 1 sepsis of stimulator. No patient had recurrence of the disease (mean follow-up 16 months), but two patients died at 3 and 8 months, respectively from anorexia and pulmonary embolism. Seven patients were available for evaluation (2 fistula, 1 death). Before training, the resting pressure and the squeeze pressure were 30 and 175 cm H2O respectively. At the time of evaluation, the electrical stimulated pressure was 95 cm H2O. Six of these 7 patients were continent (5 with spontaneous defecation, 1 with enemas) and 1 was incontinent. CONCLUSIONS: Anorectal reconstruction with dynamic graciloplasty can be an alternative to permanent colostomy for selected patients after APR. However, there is a high morbidity and the quality of life of the patients must be evaluated.     

Characteristics of aluminum-implanted 6H-SiC samples after different thermal treatments

Multiple energy aluminum (Al) implantations were performed at room temperature in n-type epitaxial 6H-SiC layers, aiming at amorphizing the material from the surface up to a depth inferior to 0.5 μm. Annealings were then carried out in an induction furnace. The goal of this paper is to optimize the furnace geometrical configuration, in order to reduce the surface degradation and improve the crystal reordering. This optimization was established for one-side amorphized wafers, which need restricting annealing parameters, and is therefore supposed to be valid for less crystal damaging implantations. Two types of geometrical parameters were essentially studied: the internal configuration, which tends to increase the silicon partial pressure inside the reactor, and the position of the sample, which has a direct influence on the recrystallization and on the dopant electrical activation. The annealings are compared for the same thermal parameters: the plateau temperature (1700 °C), the annealing duration (30 min), and the heating rate (60 °C s⁻¹). The surface roughness was evaluated by using atomic force microscopy. Two final configurations were retained, leading to satisfactory results with respect to the as-implanted material: (i) Rutherford backscattering spectrometry in channeling geometry revealed a very good recrystallization in both cases, giving a signal level similar to the virgin crystal one; (ii) secondary ion mass spectrometry showed two distinct results depending on the sample position: one position led to some material etching, especially the SiC part which was amorphized by the implantation, and the second position gave rise to the deposition of a crudely monocrystalline SiC layer on the surface of the sample implanted side. This coating was found to prevent from any dopant loss by exodiffusion or material etching. Electrical measurements (four-point probe at 300 K) proved an Al substitutional ratio of 97 and 78% depending on the configuration, giving room temperature sheet resistances of about 2×10⁴ and 4×10⁴ Ω sq.⁻¹, respectively, for 4×10¹⁹ cm⁻³ Al implanted samples.