Order and randomness in Kolmogorov-Johnson-Mehl-Avrami-type phase transitions.

The distribution of points on a 2D domain influences the kinetics of its coverage when a growth law is attached at each point. This implies that the kinetics of space filling can be adopted as a descriptor of the degree of order of the initial point distribution. In this paper, the degree of order of an initial array of points has been changed following two paths: (i) from a regular square lattice, through increasing displacement assigned to each point, towards Poissonian disorder; (ii) from a Poissonian distribution, by introducing a hard core potential with increasing correlation lengths, towards a more ordered lattice. A linear growth law has been attached to the points of the initial array and the kinetics X(X(e)), where X(e) is the extended coverage as defined in the Kolmogorov-Johnson-Mehl-Avrami model, has been monitored. The quantitative analysis has been performed by fitting the kinetics to an equation which we propose for the first time and which has proved to be, in fact, highly suitable for the purpose. The results demonstrate that the gross of variation from order to disorder is obtained for point displacements, u, of the order of a, the latter being the constant of a square lattice. Vice versa, the introduction of a correlation distance in a random distribution provokes at most an order limited to the first neighbors and no real order can ever be reached. Others descriptors have been investigated, all confirming our results. We also developed an analytical description based on the use of the f-functions, as have been defined by Van Kampen, up to the second order terms. Such a description has been shown to work well for u/a < 1 within an interval ΔX(e) which depends on the ϵ value.

Beyond the constraints underlying Kolmogorov-Johnson-Mehl-Avrami theory related to the growth laws.

The theory of Kolmogorov-Johnson-Mehl-Avrami for phase transition kinetics is subjected to severe limitations concerning the functional form of the growth law. This paper is devoted to sidestepping this drawback through the use of the correlation function approach. Moreover, we put forward an easy-to-handle formula, written in terms of the experimentally accessible actual extended volume fraction, which is found to match several types of growths. Computer simulations have been performed for corroborating the theoretical approach.

Mean field approach for describing thin film morphology.

A mean field approach is employed for determining the kinetics of two main quantities for film morphology, namely the number of islands and the film perimeter. These two quantities have been computed for both coalescence and impingement growth regimes. For each case the growth of two- and three-dimensional islands has been considered. In addition, the effect of the spatial correlation among nuclei has been taken into account on the grounds of the hard core interaction. Analytic formulae have been derived for each case.

[Study with thoracic and abdominal spiral CT in intensive care unit patients]. / Studio mediante TC spirale del torace e dell'addome nei pazienti ricoverati nei reparti di rianimazione.

INTRODUCTION: The severe clinical conditions of intensive care unit patients need frequent imaging studies to detect the pathologic changes in the patients' situation and to plan the correct therapeutic management. The yield of bedside plain radiography is often not diagnostic but moving the patients to the radiology department could affect their clinical conditions. Conventional CT is difficult to perform in these patients because they need continuous assistance and cannot cooperate during the diagnostic examination. MATERIAL AND METHODS: The authors examined with Spiral CT 46 unconscious patients in poor clinical conditions who presented a variety of pulmonary and abdominal diseases. Thirty coma patients were submitted to bedside chest radiography and then to Spiral CT because there was disagreement between the radiographic and the clinical findings. Sixteen patients with abdominal conditions underwent Spiral Ct, 11 of them after bedside US. The chest and abdomen were examined with Spiral CT in 2/16 patients and the abdomen only in 5 cases; twenty-two of 46 patients were under assisted ventilation. During all the Spiral CT studies, the patients had their arms along the body. Spiral CT results were compared with those of bedside chest radiography in 30 cases and with those of bedside abdominal US in 11 patients. DISCUSSION AND CONCLUSIONS: Spiral CT is a fast examination technique with no major artifacts which can be used safely also in unconscious patients. It confirmed a variety of pathologic conditions which may be misdiagnosed by conventional chest radiography, which improves the care of these patients. Bedside plain radiography is limited by several factors depending on the patient (no cooperation, variable respiration, still decubitus), the examination technique (X-ray projection, exposure, poor diagnostic yield), and the anatomical region of interest (mediastinal vessels). Even though our technical standard for conventional radiography was high, Spiral CT was better in detecting parenchymal consolidation and pleural effusion, a missed pneumothorax or thromboembolic disease. We always performed Spiral CT when the clinical findings did not match the results of bedside plain radiography. Moving the patients was very easy because the intensive care unit in our hospital is in the same building as the radiology department and there were dedicated devices supporting the coma patients.

An experimental study on fluorocarbons as blood substitutes.

A fluorocarbon emulsion (Fluosol DA 20%) was experimented as a blood substitute. Fourty-five rats weighing 320 +/- 30 g. underwent different degrees of hemodilution, by isovolemic exanguino-transfusions. A first group (15 rats) had maximal exchange transfusion (Ht = 0,5%) with Fluosol DA 20% and was followed for 12 hours. A second group (15 rats) (control group) underwent the same procedure, but hydrolyzed gelatin 3% (Emagel) was used instead of Fluosol DA 20%. A third group (15 rats) had partial exchange-transfusion (Ht = 23 +/- 2%) with Fluosol DA 20%, and was followed for 2 months. Cerebral and cardiovascular activity, respiratory exchanges and acid-base balance as well as other basic biological parameters were evaluated in the first and second group. The initial signs of altered cerebral activity were observed with a Ht = 2%, while death occurred at Ht = 0,5% due to respiratory arrest. In the third group, a retention of fluorocarbon particles was demonstrated by gas chromatography in all the organs examined. In this group, lung and spleen lesions were also observed by light microscopy and transmission electron microscopy.

[Artificial blood. Experimental studies on fluorocarbons as chemical blood substitutes]. / I1 sangue artificiale. Ricerche sperimentali sull'uso dei fluorocarbonati come succedanei chimici del sangue.

Fluorocarbonates are organic compounds capable of carrying oxygen and surrendering it to tissues by means of biological sound modalities. Experimentation of an emulsion consisting of perfluorotripropylamine and perfluorodecaline (Fluosol DA 20%) as a blood substitute is reported. Acute (Ht less than 1%) and chronic morphological (Ht = 15%) studies were performed on rats, and a semi-acute biochemical and morphological protocol (Ht = 21%) was experimented in pigs. The first signs of altered cerebral electrical activity occurred at Ht = 2% in the acute experiments, and death due to respiratory arrest took pace at Ht = 0.5%. In the semiacute and chronic experiments, widespread infiltration of fluorocarbonic micelles was noted on histological and electron microscope lung and liver preparations.

Morphological evaluation of the human umbilical vein graft. An experimental study.

23 human umbilical vein segments (5 mm X 4-5 cm) were implanted into the carotid and iliac arteries of 15 dogs, removed at intervals ranging from 10 to 360 days after surgery and analyzed by light and scanning electron microscopy. 10 days after implantation, a thin layer of fibrin covered the central areas of the grafts, while thick platelet aggregates were found near the anastomoses. After 30 days, the progressive connective tissue ingrowth led to the organization of a thin fibrous inner layer on which endothelial-like cells grew, spreading from both anastomoses. The endothelialization process appeared to be almost complete at 120 days after implantation, while at 360 days the flow surface was totally lined.

Scanning electron microscopy evaluation of porous and nonporous arterial substitutes.

The fate of two different kinds of new small arterial substitutes, porous and nonporous, has been compared, particularly with regard to the structure of the luminal surface. Twenty-eight weavenit Dacron pyrolytic carbon coated grafts and 28 glutaraldehyde-tanned human umbilical vein segments were implanted into the carotid arteries of dogs. Grafts were removed at intervals, from ten to 120 days after implantation, and examined by scanning electron microscopy. The cumulative patency rate was 96.4 per cent for Dacron and 85.7 per cent for umbilical vein grafts. Ten days after implantation, the Dacron grafts were uniformly covered by a thin thrombus layer, while the umbilical vein grafts showed a thin network of fibrin on the central portion of the luminal surface of the graft and thrombotic deposits at the anastomoses. Thirty days after implantation, both types of prostheses showed the development of a thin fibrous tissue layer on the inner surface. Finally, at 120 days, an endothelial lining was observed.