Alberto Vailati

A fluid or fluid mixture, subjected to a vertical temperature and/or concentration gradient in a gravitational field, exhibits greatly enhanced light scattering at small angles. This effect is caused by coupling between the vertical velocity fluctuations due to thermal energy and the vertically varying refractive index. Physically, small upward or downward moving regions will be displaced into fluid having a refractive index different from that of the moving region, thus giving rise to the enhanced scattering. The scattered intensity is predicted to vary with scattering wave vector q, as q-4, for sufficiently large q, but the divergence is quenched by gravity at small q. In the absence of gravity, the long wavelength fluctuations responsible for the enhanced scattering are predicted to grow until limited by the sample dimensions. It is thus of interest to measure the mean-squared amplitude of such fluctuations in the microgravity environment for comparison with existing theory and ground based measurements. The relevant wave vectors are extremely small, making traditional low-angle light scattering difficult or impossible because of stray elastically scattered light generated by optical surfaces. An alternative technique is offered by the shadowgraph method, which is normally used to visualize fluid flows, but which can also serve as a quantitative tool to measure fluctuations. A somewhat novel shadowgraph apparatus and the necessary data analysis methods will be described. The apparatus uses a spatially coherent, but temporally incoherent, light source consisting of a super-luminescent diode coupled to a single-mode optical fiber in order to achieve extremely high spatial resolution, while avoiding effects caused by interference of light reflected from the various optical surfaces that are present when using laser sources. Results obtained for a critical mixture of aniline and cyclohexane subjected to a vertical temperature gradient will be presented. The sample was confined between two horizontal parallel sapphire plates with a vertical spacing of 1 mm. The temperatures of the sapphire plates were controlled by independent circulating water loops that used Peltier devices to add or remove heat from the room air as required. For a mixture with a temperature gradient, two effects are involved in generating the vertical refractive index gradient, namely thermal expansion and the Soret effect, which generates a concentration gradient in response to the applied temperature gradient. For the aniline/cyclohexane system, the denser component (aniline) migrates toward the colder surface. Consequently, when heating from above, both effects result in the sample density decreasing with altitude and are stabilizing in the sense that no convective motion occurs regardless of the magnitude of the applied temperature gradient. The Soret effect is strong near a binary liquid critical point, and thus the dominant effect is due to the induced concentration gradient. The results clearly show the divergence at low q and the predicted gravitational quenching. Results obtained for different applied temperature gradients at varying temperature differences from the critical temperature, clearly demonstrate the predicted divergence of the thermal diffusion ratio. Thus, the more closely the critical point is approached, the smaller becomes the temperature gradient required to generate the same signal. Two different methods have been used to generate pure concentration gradients. In the first, a sample cell was filled with a single fluid, ethylene glycol, and a denser miscible fluid, water, was added from below thus establishing a sharp interface to begin the experiment. As time went on the two fluids diffused into each other, and large amplitude fluctuations were clearly observed at low q. The effects of gravitational quenching were also evident. In the second method, the aniline/cyclohexane sample was used, and after applying a vertical temperature gradient for several hours, the top and bottom temperatures were set equal and the thermal gradient died on a time scale of seconds, leaving the Soret induced concentration gradient in place. Again, large-scale fluctuations were observed and died away slowly in amplitude as diffusion destroyed the initial concentration gradient.

The aim of the study was to analyze the frequency of incidental thyroid carcinoma (unknown tumor smaller than or equal to 10 mm) in a consecutive series of 462 total thyroidectomies for multinodular goiter and to investigate the clinical risk factors for this type of malignancy. A retrospective, single-center study of outcome data collected from patients with preoperative diagnosis of multinodular goiter who underwent total thyroidectomy at the General Surgery Unit of Pavia (Italy) between January 2000 and December 2008 was performed. Possible risk factors for malignancy were: gender, age, time of evolution of goiter, presence of a dominant nodule in multinodular goiter, hyperthyroidism, history of radiation to the neck, residence in an area of endemic goiter, prior thyroid surgery, calcifications in the goiter detected by neck ultrasound or chest X-rays, and a family history of thyroid diseases. In a 9-year period, 462 patients underwent total thyroidectomy. We found 41 cases of incidental thyroid carcinoma; the most common histopathological type was papillary. The multivariable analysis demonstrated that the clinical variables associated with occult carcinoma were a personal history of radiation therapy to the neck, the presence of calcifications detected by ultrasound or neck X-rays, and a family history of thyroid diseases; residence in an area of endemic goiter was a protective factor. A personal history of radiation to the neck, detection of calcifications by ultrasound or by neck X-rays, and a family history of thyroid diseases should be considered clinical risk factors for malignancy in multinodular goiter.

Heat convection in water can be suppressed by adding a small amount of highly thermophilic nanoparticles. We show that such suppression is not effective when a suspension with uniform concentration of nanoparticles is suddenly heated from below. At Rayleigh numbers smaller than a sample dependent threshold Ra;{*} we observe transient oscillatory convection. Unexpectedly, the duration of convection diverges at Ra;{*}. Above Ra;{*} oscillatory convection becomes permanent and the heat transferred exhibits bistability. Our results are explained only partially and qualitatively by existing theories.

Convection in an inclined layer of fluid is affected by the presence of a component of the acceleration of gravity perpendicular to the density gradient that drives the convective motion. In this work we investigate the solutal convection of a colloidal suspension characterized by a negative Soret coefficient. Convection is induced by heating the suspension from above, and at large solutal Rayleigh numbers (of the order of 10(7)-10(8)) convective spoke patterns form. We show that in the presence of a marginal inclination of the cell as small as 19 mrad the isotropy of the spoke pattern is broken and the convective patterns tend to align in the direction of the inclination. At intermediate inclinations of the order of 33 mrad ordered square patterns are obtained, while at inclination of the order of 67 mrad the strong shear flow determined by the inclination gives rise to ascending and descending sheets of fluid aligned parallel to the direction of inclination.

It is well known that coeliac disease is associated with autoimmune endocrine diseases, such as autoimmune thyroid disease and insulin-dependent diabetes mellitus. Recently, coeliac disease has been shown in approximately 10% of patients with autoimmune Addison's disease. Addison's disease is the most common cause of primary adrenocortical insufficiency and it shares several clinical features with coeliac disease. Although hyperpigmentation and hypotension are the most specific signs, gastrointestinal symptoms are common and can be the first complaints of the patients. The aim of our study was to investigate the prevalence of coeliac disease in Italian patients with Addison's disease. Seventeen consecutive patients affected by Addison's disease (14 F, mean age 53.9 years, range 26-79 years) were enrolled in the study. Eleven of them were affected by Addison's disease associated with autoimmune thyroid disease and/or insulin-dependent diabetes mellitus; the other 6 patients were suffering from isolated Addison's disease. Diagnosis had been performed at the age of 40.5 years (range 23-55). Steroid treatment had already been started in 16 of the patients. Endomysial antibodies were tested in all of them and a duodenal biopsy was taken in those found to be positive for antiendomysial antibody (EMA). One out of 17 patients was found to be EMA positive. Duodenal biopsy confirmed the diagnosis of coeliac disease by showing subtotal villous atrophy. Although we studied only a small sample, our preliminary results confirmed that Addison's disease is associated with coeliac disease, being present in 5.9% of patients with Addison's disease. Since the symptoms can be similar and treatment of Addison's disease can mask coeliac disease, this association should always be actively investigated.