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L Renna

Publications and source records attributed to L Renna.

4 recordsLinked to original sources

Asymmetrical dripping.

Dripping from a faucet is studied, where by cutting diagonally the tip breaks the cylindrical symmetry. We measured long dripping time series recorded with a laser-beam apparatus and continuous change in drop position using a high-speed camera. It is found that the added degree of freedom produces a transversal oscillation of a pending drop, which couples with a vertical oscillation induced by the breaking off of the previous drop. As a consequence dripping times shorten and dripping patterns regularize. The effect is attributed to the "reduced" contact circle and to decreased frequency of the vertical oscillations of the residue. A very complex flow circulation pattern within the forming drop is observed. It is suggested that geometrical shape vibrations of the pending drop take place by the development of eddies of different amount, more effective in the vicinity of the highest edge of the tip, where they dissipate more slowly. This asymmetrical liquid flow is brought about by the slanting form of the orifice and overlaps with the axial oscillations.

Journal Article↗

Experimental study of dripping dynamics.

The dependence of dripping dynamics from physical properties of the nozzles is investigated. The analysis is performed by means of two complementary methods: (i) long dripping time series recorded with a standard laser-beam apparatus; and (ii) drop formations observed with a fast digital camcorder. Dripping from nozzles of different sizes is analyzed, and the formation of satellite drops is related to the preeminent physical parameter of control (flow rate). Quasielastic collisions between parent and satellite drops are observed.

Journal Article↗

Mass on a spring map for the dripping faucet at low flow rates.

An improved discrete map for the mass-on-a-spring model for the dripping faucet is used to reproduce the evolution of experimental dripping spectra at low flow rates. If an inverse dependence of drop mass on flow rate is supposed, a repeated evolution from period 1 to chaos is obtained. A comparison between discrete relaxation oscillator attractors and dissipative type-web map attractors is carried out. It is found that a dissipative web map accounts for some characteristics of the relaxation oscillator map, thus giving further tools for investigation.

Journal Article↗

Programmed cell death in colorectal carcinogenesis.

The most studied mechanism of malignant transformation has been cell proliferation. The relationship between programmed cell death (apoptosis), cell proliferation, and apoptosis regulatory genes (p53 and bcl-2), was studied in normal colonic epithelium, 26 sporadic adenomas both early and late, 25 FAP adenomas, and 34 carcinomas. We showed a decrease in programmed cell death and an increase in cell proliferation during the transition from adenoma to carcinoma. The increase of expression of p53 from early (10%) to late adenomas (87%) contrasted with the decrease of bcl-2 staining. Sixty-two per cent and 23% of carcinomas were reactive for p53 and bcl-2 respectively. Abnormal early activation of the bcl-2 gene, rather than late p53 gene mutation appears to be responsible for inhibition of apoptosis in colorectal carcinogenesis. bcl-2 was higher in FAP adenomas than in sporadic cases, and in carcinomas favouring the accumulation of long-living cells, which are more subject to mutation and thus cancerization.

Apoptosis↗