Peripheral mixing of passive scalar at small Reynolds number

Mixing of a passive scalar in the peripheral region close to a wall is investigated by means of accurate direct numerical simulations of both a three-dimensional Couette channel flow at low Reynolds numbers and a two-dimensional synthetic flow. In both cases, the resulting phenomenology can be understood in terms of the theory recently developed by Lebedev and Turitsyn [Phys. Rev. E 69, 036301, 2004]. Our results prove the robustness of the identified mechanisms responsible for the persistency of scalar concentration close to the wall with important consequences in completely different fields ranging from microfluidic applications to environmental dispersion modeling.Comment: 4 pages, 5 figure

Large-scale confinement and small-scale clustering of floating particles in stratified turbulence

We study the motion of small inertial particles in stratified turbulence. We derive a simplified model, valid within the Boussinesq approximation, for the dynamics of small particles in presence of a mean linear density profile. By means of extensive direct numerical simulations, we investigate the statistical distribution of particles as a function of the two dimensionless parameters of the problem. We find that vertical confinement of particles is mainly ruled by the degree of stratification, with a weak dependency on the particle properties. Conversely, small scale fractal clustering, typical of inertial particles in turbulence, depends on the particle relaxation time and is almost independent on the flow stratification. The implications of our findings for the formation of thin phytoplankton layers are discussed.Comment: 5 pages, 6 figure

Point-particle method to compute diffusion-limited cellular uptake

We present an efficient point-particle approach to simulate reaction-diffusion processes of spherical absorbing particles in the diffusion-limited regime, as simple models of cellular uptake. The exact solution for a single absorber is used to calibrate the method, linking the numerical parameters to the physical particle radius and uptake rate. We study configurations of multiple absorbers of increasing complexity to examine the performance of the method, by comparing our simulations with available exact analytical or numerical results. We demonstrate the potentiality of the method in resolving the complex diffusive interactions, here quantified by the Sherwood number, measuring the uptake rate in terms of that of isolated absorbers. We implement the method in a pseudo-spectral solver that can be generalized to include fluid motion and fluid-particle interactions. As a test case of the presence of a flow, we consider the uptake rate by a particle in a linear shear flow. Overall, our method represents a powerful and flexible computational tool that can be employed to investigate many complex situations in biology, chemistry and related sciences.Comment: 13 pages, 13 figure

Oral amelanotic melanoma: a case report

Objectives. Primary oral melanoma is a very rare malignancy, representing about 0.5% of all melanomas, characterized by a wide clinical-histological variability and a very aggressive behavior. Aim of the present study is to describe a case of oral amelanotic melanoma, an infrequent variant with a poorer prognosis than that of pigmented melanomas for a more aggressive biological behavior and frequent delays for the correct diagnosis and for starting the treatment. Case report. A 53-year-old white man referred at the Department Surgical, Oncological and Oral Sciences for a macular, scarsely pigmented lesion with irregular margins, located on anterior region of hard palate. The lesion, completely asymptomatic and without any history of trauma or injury, was observed by his dentist some months ago. The patient was a smoker (about 20 cigarettes a day for 30 years) and his anamnesis was negative for any systemic diseases and drug assumption. Histological examination, following the incisional biopsy, showed the hyperplasia of the junctional melanocytes with occasionally dendritic appearance and light atypia; on the recommendation of pathologist, a second incisional biopsy was performed, and a definitive diagnosis of “amelanotic melanoma in situ” was confirmed. After diagnosis, the patient was referred to the unit of Head and Neck Surgery for staging and surgical approach of the lesion. Conclusions. This case report underlines the importance to perform biopsy of all lesions of the oral cavity to rule out malignancy, even when slightly colored, asymptomatic and with a clinically harmless presentation. Besides benign diseases (e.g melanotic macules, nevi, extravasation of blood pigments, amalgam tattoos and deposition of other exogenous/endogenous pigments), rare variant of non-pigmented melanoma should be considered in order to avoid a dangerous diagnostic and therapeutic delay

A New Strategy for Treatment of a Congenital Arteriovenous Fistula of the Neck. Case Report

AbstractCongenital arteriovenous fistulas (AVF) without associated vascular malformations are uncommon. Only a very few cases of AVF have been reported in the neck. We describe our findings in a patient with AVF treated by a combined vascular and endovascular approach

Regulation of Expression of Cannabinoid CB2 and Serotonin 5HT1A Receptor Complexes by Cannabinoids in Animal Models of Hypoxia and in Oxygen/Glucose-Deprived Neurons

Background: Cannabidiol (CBD) is a phytocannabinoid with potential in one of the most prevalent syndromes occurring at birth, the hypoxia of the neonate. CBD targets a variety of proteins, cannabinoid CB2 and serotonin 5HT1A receptors included. These two receptors may interact to form heteromers (CB2-5HT1A-Hets) that are also a target of CBD. Aims: We aimed to assess whether the expression and function of CB2-5HT1A-Hets is affected by CBD in animal models of hypoxia of the neonate and in glucose- and oxygen-deprived neurons. Methods: We developed a quantitation of signal transduction events in a heterologous system and in glucose/oxygen-deprived neurons. The expression of receptors was assessed by immuno-cyto and -histochemistry and, also, by using the only existing technique to visualize CB2-5HT1A-Hets fixed cultured cells and tissue sections (in situ proximity ligation PLA assay). Results: CBD and cannabigerol, which were used for comparative purposes, affected the structure of the heteromer, but in a qualitatively different way; CBD but not CBG increased the affinity of the CB2 and 5HT1A receptor-receptor interaction. Both cannabinoids regulated the effects of CB2 and 5HT1A receptor agonists. CBD was able to revert the upregulation of heteromers occurring when neurons were deprived of oxygen and glucose. CBD significantly reduced the increased expression of the CB2-5HT1A-Het in glucose/oxygen-deprived neurons. Importantly, in brain sections of a hypoxia/ischemia animal model, administration of CBD led to a significant reduction in the expression of CB2-5HT1A-Hets. Conclusions: Benefits of CBD in the hypoxia of the neonate are mediated by acting on CB2-5HT1A-Hets and by reducing the aberrant expression of the receptor-receptor complex in hypoxic-ischemic conditions. These results reinforce the potential of CBD for the therapy of the hypoxia of the neonate