Starshapedness of level sets of solutions to elliptic PDEs

We investigate how some geometric properties of the domain are inherited by level sets of solutions of elliptic equations. In particular we prove that, under suitable assumptions, solutions of elliptic Dirichlet problems in starshaped rings have starshaped level sets. Our results are applicable to a large class of operators, including fully-nonlinear ones.     

Comparative LC Enantioseparation of Novel PPAR Agonists on Cellulose- and Amylose-Based Chiral Stationary Phases

The LC enantiomeric separation of several dual PPARα/γ agonists on the commercially available Chiralcel OD and Chiralpak AD columns has been evaluated in normal phase mode using a mobile phase consisting in a mixture of n-hexane, 2-propanol and trifluoroacetic acid at constant volume ratio. Most compounds were separated as underivatized acids without requiring time consuming analysis. Some complementary selectivity was evidenced on the two investigated chiral stationary phases related to the different accessibility of the active sites of the helical cavities. Additional information on the chiral recognition mechanism were deduced from the chromatographic behaviour of some selected methyl esters.     

Performance of an active well coincidence counter for HEU samples

Neutron coincidence counting is the reference NDA technique used in nuclear safeguards to measure the mass of nuclear material in samples. For high-enriched uranium (HEU) samples active neutron interrogation is generally performed and the most common device used by nuclear inspectors is the Active Well Coincidence Counter (AWCC).Within her master thesis at the Polytechnic of Milan, the first author performed an intensive study on the characteristics and performances of the AWCC in order to assess the ²³⁵U mass in HEU oxide samples at the PERLA laboratory of JRC. The work has been summarised in this paper that starts with the optimisation of the use of AWCC for nuclear safeguards, describing the calibration procedure, reporting results of a series of verification measurements, summarising the performances that can be obtained with this instruments during inspections at fuel production plants and concluding with the discussion of uncertainties related to these measurements.     

Gravitational field-flow fractionation of human hemopoietic stem cells

New cell sorting methodologies, which are simple, fast, non-invasive, and able to isolate homogeneous cell populations, are needed for applications ranging from gene expression analysis to cell-based therapy. In particular, in the forefront of stem cell isolation, progenitor cells have to be separated under mild experimental conditions from complex heterogeneous mixtures prepared from human tissues. Most of the methodologies now employed make use of immunological markers. However, it is widely acknowledged that specific markers for pluripotent stem cells are not as yet available, and cell labelling may interfere with the differentiation process. This work presents for the first time gravitational field-flow fractionation (GrFFF), as a tool for tag-less, direct selection of human hematopoietic stem and progenitor cells from cell samples obtained by peripheral blood aphaeresis. These cells are responsible to repopulate the hemopoietic system and they are used in transplantation therapies. Blood aphaeresis sample were injected into a GrFFF system and collected fractions were characterized by flow cytometry for CD34 and CD45 expression, and then tested for viability and multi-differentiation potential. The developed GrFFF method allowed obtaining high enrichment levels of viable, multi-potent hematopoietic stem cells in specific fraction and it showed to fulfil major requirements of analytical performance, such as selectivity and reproducibility of the fractionation process and high sample recovery.     

Vector magnetisation measurements on thermally evaporated CoCr multilayers and solid solutions for spintronic applications

Structure, morphology and magnetic properties of thermally evaporated Co/Cr multilayers and of the solid solution obtained by isothermal treatment of the layered samples have been studied to evaluate their potential application as high-coercivity materials for hard spin injectors in spintronic devices such as magnetic tunneling junctions. The thermal treatment was performed in a partial pressure of inert gas to allow interdiffusion of Cr and Co. Structure and composition of the materials, as well as the effects of the annealing treatment, have been investigated by field emission scanning electron microscopy and energy-dispersive X-ray analysis. The magnetic configuration of these films was investigated by magnetic force microscopy. Simultaneous measurements of two mutually perpendicular magnetisation components were performed by means of a vector vibrating sample magnetometer, and showed that the in-plane coercivity can be increased by proper thermal treatment from less than 10 Oe to about 240 Oe. However, annealing may result in a loss of compositional and morphologic homogeneity of the films.     

Photocatalytic activity of nanostructured TiO2 films produced by supersonic cluster beam deposition

The photocatalytic activity of thin, nanostructured films of titanium dioxide, synthesized by supersonic cluster beam deposition (SCBD) from the gas phase, has been investigated employing the photodegradation of salicylic acid as test reaction. Because of the low deposition energy, the so-deposited highly porous TiO₂ films are composed of nanoparticles maintaining their original properties in the film, which can be fully controlled by tuning the deposition and post-deposition treatment conditions. A systematic investigation on the evolution of light absorption properties and photoactivity of the films in relation to their morphology, determined by AFM analysis, and phase composition, determined by Raman spectroscopy, has been performed. The absorption and photocatalytic activity of the nanostructured films in the visible region could be enhanced either through post-deposition annealing treatment in ammonia containing atmosphere or employing mild oxidation conditions, followed by annealing in N₂ at 600 °C.