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

RESTITUTIO AD INTEGRUM IN A CASE OF ONJ RELATED TO BEVACIZUMAB

Aim. Bevacizumab is a humanized recombinant monoclonal antibody that blocks vascular endothelial growth factor (VEGF). The activity of VEGF is the ability to promote the vascular endothelial cells proliferation inducing the formation of new blood vessels. Bevacizumab is used in the treatment of selected advanced colon, lung, renal and central nervous system tumours and plays a developing role in the management of breast and ovarian cancers. It is also injected intraocularly for treatment of macular degeneration. Recently, bevacizumab has been reported as responsible of drug-related osteonecrosis of the jaw (ONJ), showing a histological pattern similar to bisphosphonate-related ONJ. Moreover, it may increase the risk for osteonecrosis of the jaw when administered in isolation or when given concurrently with bisphosphonates. Materials and methods. Only few case reports in literature have been reported describing ONJ after bevacizumab administration. In June 2011, a 57-year-old female patient was referred to our department for pain in the left posterior mandibular region. She reported the following anamnestic data: in 2002, for the diagnosis of breast cancer, she underwent to left quadrantectomy and radiant treatment; from October 2010, she was receiving multimodal chemotherapy containing bevacizumab. No previous treatment with bisphosphonates, or other known local and systemic risk factors were reported. Intraoral examination showed a painful area of bone exposure in the left posterior lingual mandible. The surrounding soft tissue was erythematous with purulent discharge and with swelling of the extraoral soft tissue of the left mandible. After interaction with her oncologist, bevacizumab has been suspended and systemic antibiotic (ampicillina/sulbactam intramuscularly twice daily for 8 days and metronidazole 250mg per os twice daily for 8 days), local antiseptics (chlorhexidine 0.2% mouth rinses and 0.5% chlorhexidine gel) were administered. Results. After 15 days, she showed a complete healing after spontaneous sequestration of a necrotic bone fragment. Conclusions. The antiangiogenic and antiresorptive effects of bevacizumab are dose-dependent and time-dependent. Probably this implies that angiogenesis, bone remodelling and healing processes should restart after drug cessation. The present case supports the necessity to apply BRONJ prevention protocol also in patients in therapy with bevacizumab

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

Short-term memory effects on visual global/local processing in tufted capuchin monkeys (Sapajus spp.).

Nonhuman primates, differently from humans, are less proficient at processing global properties of visual compound stimuli. It has been suggested that humans preferentially process stimuli globally because this enables a more economical encoding of the stimuli. In this study we assessed the role of short-term memory (STM) in global/local processing by presenting tufted capuchin monkeys with Navon-type hierarchical figures in both simultaneous and delayed matching-to-sample tasks. Capuchins’ ability to discriminate hierarchical stimuli was evaluated as a function of increasing delay intervals (0.0, 0.5, 1.0, 2.0 and 3.0 sec) between the disappearance of the sample and the presentation of the comparison stimuli. The results showed that recognition accuracy for local features was above chance level with delays of up to 3.0 sec, as previously reported when capuchins were faced with nonhierarchical stimuli. By contrast, the recognition of global configurations was above chance level in simultaneous, 0.0 and 0.5 sec delay conditions but not at delay intervals of 1.0 sec or longer. These findings indicate that capuchins’ propensity to process the local properties of visual stimuli can be observed when a delay is interposed between the presentation of sample and comparison stimuli and was not reversed by increasing the delay. Moreover, our results show that capuchins’ local propensity was not reversed by increasing stimulus size. Overall, our study confirms crucial differences between human and nonhuman primates and adds new insights into the comparative research on visual grouping functions of these species