Boost-chopper-derived PFC rectifiers: interest and reality

This work presents an overview of single-phase boost-chopper-derived power-factor-correction rectifiers. Converters are presented for several control strategies in continuous and discontinuous current mode operations. The presentation highlights the main characteristics of the converters and underlines harmonic content over a wide frequency range. A methodology is derived to compute these harmonics in order to facilitate the analysis and performance evaluation of the converters. Based on this methodology, a comparison is conducted in order to highlight advantages and drawbacks of the most popular converters and control strategies. A table is given where main converter critical parameters are summarized in order to help the designer, in converter and operating mode selections. Practical results are provided to validate the modeling technique.     

Accelerated Shift-and-Add Algorithms

The problem addressed in this paper is the computation of elementary functions (exponential, logarithm, trigonometric functions, hyperbolic functions and their reciprocals) in fixed precision, typically the computer single or double precision. The method proposed here combines Shift-and-Add algorithms and classical methods for the numerical integration of ODEs: it consists in performing the Shift-and-Add iteration until a point close enough to the argument is reached, thus only one step of Euler method or Runge-Kutta method is performed. This speeds up the computation while ensuring the desired accuracy is preserved. Time estimations on various processors are presented which illustrate the advantage of this hybrid method.     

Quantitative and kinetic evolution of wound healing through image analysis

To define a healing function based on parameters measured on digitized images of wounds, and to use it to compare the rate of healing of two skin graft donor sites, one treated with petrolatum gauze (Pg) and the other with a topical preparation containing alginates (A). Digital photographs of donor sites (depth 0.6 mm) taken every two days between day 6 and day 12 were analyzed blind using the same algorithm, following changes in color and homogeneity. Analysis of variance was used to identify those parameters that changed during healing. The healing function was constructed using measurements made in six patients (group 1) randomly chosen from ten requiring skin grafts, and was applied and validated using data from the remaining four patients (group 2). The results given by this healing function were compared with those provided by principal component analysis. The most significant healing parameters were those measuring wound homogeneity, and our healing function reflects how these change with time. The time-dependent curves of the function calculated for groups 1 and 2 matched well enough to be considered as being derived from the same set of measurements. The results given by this healing function explained, by analogy, the meaning of the first principal component of principal component analysis. From day 6 to day 12, the healing function followed the same time-course for the Pg and A treatments, but healing was achieved significantly earlier (4 days, p < 0.03) with A. This suggests that the effect of A on wound healing is achieved in the first six days, before the visual changes from epidermalization are analyzable.     

Lipoma of the superficial lobe of the parotid gland. A case report

We report the case of a patient with a lipoma of the superficial lobe of the right parotid gland. Lipomas of the parotid gland are very rare. They are said to constitute one to two percent of all parotid tumours. Only six cases were found in the recent literature. Preoperative diagnosis is difficult when the physical examination reveals a renitent, well-localized and painless mass. However, magnetic resonance imaging is now the imaging modality of choice to facilitate the diagnosis, but the diagnosis can only be confirmed by histological examination of the tumour. We discuss the value of superficial parotidectomy, while some authors suggest an enucleation of lipomas of the superficial lobe of parotid.     

First Operation of the CERN UA1 Central Detector

The Central Detector of the UA1 experiment at the CERN pp? Collider underwent a first physics run at the end of 1981. The detector consists of a large drift chamber assembly (25 m3, ~ 6000 sense wires). An electronics readout with multi-hit capability simultaneously digitizes the time and the analog information used for charge division and energy measurement. The initial performance of the readout and control system will also be presented. The detector was tested in two cosmic-ray runs, and is now fully operational for the second physics run; this started at the beginning of October 1982.     

Potato Starch Encapsulation with Polyethylene. I. Catalysis and Polymerization

A process for the encapsulation of individual potato starch granules with polyethylene is described. It involves a thorough dessication of starch followed by a generation of a fine precipitate of VCl₃ which adsorbs on the surface of each granule. When this deposit of VCl₃ is activated by Al(C₂H₅)₃, the surface of the granule becomes active toward polymerization of ethylene. An encapsulation of each individual granule by polyethylene is obtained when the polymerization occurs in a non solvent. The growth of the encapsulation shell is studied as function of time, temperature, catalyst concentration and moisture content of the starch samples.     

Effect of electrostatic interaction on phase separation behaviour of chitin crystallite suspensions

Optical and electron microscopy were used to observe the dynamics of the phase separation in aqueous chitin suspensions prepared by HCl hydrolysis of crab chitin. Freeze-fracture transmission electron microscopy reveals that chitin crystallites are partially aggregated in the suspension and have an average length of 200 nm and an average width of 8 nm. They exhibit a positive surface charge of approximately 0.5 e/nm2 when fully protonated. The liquid crystal-forming aqueous suspensions of such crystallites are investigated through phase diagrams and Zeta potential measurements for different ionic strength. Exposure of the suspension to a low concentration of univalent electrolyte has a negligible effect on phase separation because of the contribution of the charged crystallites themselves to the ionic strength. The thickness of the effective repulsive layer is estimated both from the phase diagrams according to Onsager's theory and from the computed interaction energy derived from the Poisson-Boltzmann equation using the experimental Zeta potential as surface potential. When the contribution of crystallites to the ionic strength is taken into account and an hypothetical linear charge density close to the Manning limit is assumed, there is good agreement with the Debye length.     

Fixed post-traumatic flexion-contractures of digits. Review of thirty-three cases

A fixed post-traumatic flexion contracture of a finger is usually secondary to multiple previous operations. We have observed that a former flexor tendon laceration is not constant and is missing in 18% of our cases. The flexor tendons are, nevertheless, always involved in the contracture. A volar skin contracture was present in all cases, but only in half of them was noted a retraction of the volar components of the PIP joint. This articular involvement has no statistical correlation with the time elapsed from the onset of the contracture. We have reviewed 33 cases of post-traumatic flexions contractures of the digits all secondary to volar trauma. In every case there was at least a flexor tendon adhesion and skin contracture. They have all been submitted to both objective and statistical analysis. Results have been evaluated by comparison between the normal functional range of motion for each digit and the actual post-operative active range of motion. On the basis of our study we conclude that the age of the patient is an important prognostic factor. We obtained 75% satisfactory results in patients younger than 27 years, but only 22% in the older group. Good results are more easily obtained in radial (65%) than ulnar digits (31%). While the authors rated 39% of the results bad, half of the patients in this group were satisfied with the result. A volar PIP joint release has been necessary in half of the cases with no significant secondary joint stiffness. A skin flap is necessary to cover the cutaneous defect secondary to the release. There is no statistically significant advantage to cross finger flaps. Therefore we feel that local flaps are indicated except in the cases where local scar tissues would not make it, feasible. The prognosis is independent of the number of previous operations and of associated nerve lesions. Therefore amputation is not the only solution for a multi-operated finger fixed in flexion.