Standing wave in evaporating meniscus detected by infrared thermography

A standing wave has been detected in the evaporating meniscus formed on an organic liquid (acetone) inside a horizontally positioned capillary tube of 1mm internal diameter. The standing wave is believed to originate from the interaction between surface tension and gravitational forces. We found that the standing wave ensues only at the upper part of the meniscus interface where gravity and surface tension act in the opposite direction. This experimental observation is similar to standing waves observed in floating zones in microgravity but different from travelling waves reported recently in volatile drops; in both cases the waves are produced by temperature differences along a liquid-vapour interface. By employing InfraRed thermography, we recorded the temperature distribution of the meniscus interface, and we found that the first characteristic frequency of the standing wave is around 0.3Hz.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Poly(styrene-co-butadiene) Random Copolymer Thin Films and Nanostructures on a Mica Surface: Morphology and Contact Angles of Nanodroplets

The self-assembly of poly(styrene-co-butadiene) random copolymers on mica surfaces was studied by varying solution concentrations and polymer molecular weights. Toluene solutions of the poly(styrene-co-butadiene) samples were spin coated onto a mica surface and the resulting polymer morphology was investigated by atomic force microscopy. At higher concentrations, thin films formed with varying thicknesses; some dewetting was observed which depended on molecular weight. Total dewetting did not occur despite the polymer’s low glass transition temperature. Instead, partial dewetting was observed suggesting the polymer was in a metastable equilibrium state. At lower concentrations, spherical cap shaped nanodroplets formed with varying sizes from single polymer chains to aggregates containing millions of chains. As molecular weight was increased, fewer aggregates were observed on the surface, albeit with larger sizes resulting from increased solution viscosities and more chain entanglements at higher molecular weights. The contact angles of the nanodroplets were shown to be size dependent. A minimum contact angle occurs for droplets with radii of 100 nm – 250 nm at each molecular weight. Droplets smaller than 100 nm showed a sharp increase in contact angle; attributed to an increase in elastic modulus of the droplets, in addition, to a positive line tension value. Droplets larger than 250 nm also showed an increased contact angle due to surface heterogeneities which cannot be avoided for larger droplets. This increase in contact angle plateaus as the droplet size reaches the macroscopic scale

Goodbye Hartmann trial: a prospective, international, multicenter, observational study on the current use of a surgical procedure developed a century ago

Background: Literature suggests colonic resection and primary anastomosis (RPA) instead of Hartmann's procedure (HP) for the treatment of left-sided colonic emergencies. We aim to evaluate the surgical options globally used to treat patients with acute left-sided colonic emergencies and the factors that leading to the choice of treatment, comparing HP and RPA. Methods: This is a prospective, international, multicenter, observational study registered on ClinicalTrials.gov. A total 1215 patients with left-sided colonic emergencies who required surgery were included from 204 centers during the period of March 1, 2020, to May 31, 2020. with a 1-year follow-up. Results: 564 patients (43.1%) were females. The mean age was 65.9 ± 15.6 years. HP was performed in 697 (57.3%) patients and RPA in 384 (31.6%) cases. Complicated acute diverticulitis was the most common cause of left-sided colonic emergencies (40.2%), followed by colorectal malignancy (36.6%). Severe complications (Clavien-Dindo ≥ 3b) were higher in the HP group (P < 0.001). 30-day mortality was higher in HP patients (13.7%), especially in case of bowel perforation and diffused peritonitis. 1-year follow-up showed no differences on ostomy reversal rate between HP and RPA. (P = 0.127). A backward likelihood logistic regression model showed that RPA was preferred in younger patients, having low ASA score (≤ 3), in case of large bowel obstruction, absence of colonic ischemia, longer time from admission to surgery, operating early at the day working hours, by a surgeon who performed more than 50 colorectal resections. Conclusions: After 100 years since the first Hartmann's procedure, HP remains the most common treatment for left-sided colorectal emergencies. Treatment's choice depends on patient characteristics, the time of surgery and the experience of the surgeon. RPA should be considered as the gold standard for surgery, with HP being an exception

EXPERMENTAL INVESTIGATION OF A TRANSPARENT SINTERED HEAT PIPE

info:eu-repo/semantics/publishe

Self-induced Marangoni flow in evaporating alcoholic solutions

The self-induced Marangoni convection in alcoholic solutions is the subject of the present experimental investigation. Pure ethanol and its mixtures with 5%, 10% and 20% in weight of water are presented and discussed. In particular, Marangoni flow in horizontal pipes from 100 to 1000 μm inner diameter is studied. Vortex spinning frequency, average particle tracers velocity and evaporation rate are measured and discussed. The evaporation rate increases and the evaporation flux decreases at bigger tube sizes in line with previous investigations; pure ethanol has higher evaporation rate and flux than ethanol/water mixtures. The spinning frequency and the average tracer particles velocity decrease for increasing water content in the mixtures. All of these findings are due to evaporative cooling effect which is higher at the meniscus wedge (where the triple-line region is found) than at the meniscus center; this causes a difference in temperature between the wedge and the center that generates a gradient of surface tension driving vigorous Marangoni convection, that has been reported and analyzed. The experimental results are explained on the basis of a numerical model including evaporation, vapor diffusion, heat and mass transfer from the liquid to the surrounding ambient and the Marangoni effects