Scaling, Optimality, and Landscape Evolution

A nonlinear model is studied which describes the evolution of a landscape under the effects of erosion and regeneration by geologic uplift by mean of a simple differential equation. The equation, already in wide use among geomorphologists and in that context obtained phenomenologically, is here derived by reparametrization invariance arguments and exactly solved in dimension d=1. Results of numerical simulations in d=2 show that the model is able to reproduce the critical scaling characterizing landscapes associated with natural river basins. We show that configurations minimizing the rate of energy dissipation (optimal channel networks) are stationary solutions of the equation describing the landscape evolution. Numerical simulations show that a careful annealing of the equation in the presence of additive noise leads to configurations very close to the global minimum of the dissipated energy, characterized by mean field exponents. We further show that if one considers generalized river network configurations in which splitting of the flow (i.e., braiding) and loops are allowed, the minimization of the dissipated energy results in spanning loopless configurations, under the constraints imposed by the continuity equations. This is stated in the form of a general theorem applicable to generic networks, suggesting that other branching structures occurring in nature may possibly arise as optimal structures minimizing a cost function.     

Analysis of plasma free fatty acid cyanomethyl derivatives by GC-NPD for the diagnosis of mitochondrial fatty acid oxidation disorders

Summary Early diagnosis of fatty acid oxidation (FAO) disorders is important to reduce severe morbidity and mortality. Although analysis of plasma free fatty acids (FFAs) is frequently performed using stable isotope-dilution gas chromatography-mass-spectrometry (GC-MS), there are institutions where the required instrumentation is not available to support a rapid work-up of acutely ill patients. For this reason, we have developed a novel cyanomethyl derivatization method for FFAs which is followed by GC analysis of the resulting esters using nitrogen-phosphorus detector (NPD) for the rapid diagnosis of mitochondrial fatty acid oxidation disorders. FFAs were extracted from plasma and derivatized to the cyanomethyl ester by heating with bromoacetonitrile at 60°C for 30 min GC-NPD analysis was then performed. The mean recoveries of C6:0-C18:0FFAs were between 87% abd 96%. The method detection limits (S/N=3) were 0.1–0.5 ng for C6:0-C14:0 FFAs, and 0.001–0.01 ng for C16:0-C18:0 FFAs. We succesfully performed differential diagnosis of representative FAO disorders from the confimed patient's plasmas. This simple method offers cost-effective and time-saving alternative to GC-MS for the biochemical diagnosis of selected FAO disorders.     

A contact process with a single inhomogeneous site

The one-dimensional basic contact process is a Markov process for which particles give birth on vacant nearest neighbor sites at rate >0 and particles die at rate one. We introduce a one-dimensional contact process with a single inhomogeneous site: the evolution is as above except that a particle located at the origin does not die. Let _c be the critical value of the basic contact process. We show that for _c the upper invariant measures of the inhomogeneous contact process and the basic contact process coincide except at a finite number of sites. The behavior at = _c is much more intersting: the upper invariant measure of the inhomogeneous contact process concentrates on configurations with infinitely many particles, while it is known that the critical basic contact process dies out. So a single inhomogeneity may provoke a perturbation unbounded in space. As a byproduct of our analysis we prove that the connectivity probabilities of the critical basic contact process are not summable. We also give a biological interpretation of this model.     

Lipid composition-dependent incorporation of multiple membrane proteins into liposomes

Membrane proteins from bacteria Pasteurella multocida were used as a model for studying its incorporation into liposomes. An important step to achieve efficient high yield protein incorporation in proteoliposomes is the study of the more suitable lipid composition. To this end, we compared the amount of total protein, reconstituted by co-solubilization methods, into liposomes of phospholipids with different polar head groups and acyl chain lengths. The liposomes and proteoliposomes were characterised by isopycnic centrifugation in sucrose gradient and by dynamic light scattering. Experimental and theoretical results were compared considering the effects exerted through the hydrocarbon chain length, volume, and optimal cross-sectional area of the phospholipid (combined in the geometrical critical packing parameter, lipid–protein matching), critical spontaneous radius of curvature of the bilayer vesicle, phase transition temperature of the lipid and ratio of lipid–protein molecules present in the vesicles. The highest incorporation of multiple proteins was found with dipalmitoylphosphatidylcholine (DPPC), reaching a yield of 93% compared to the lower relative amounts incorporated in proteoliposomes of the other lipids. The incorporation of multiple proteins induces a proportional enhancement of vesicular dimension, since DPPC–proteoliposomes have an average diameter of 1850 Å, compared to the 1430 Å for pure DPPC vesicles.     

TIME-GATED FLUORESCENCE IMAGING FOR THE DIAGNOSIS OF TUMORS IN A MURINE MODEL

A system for time-gated fluorescence imaging was used to perform measurements on tumor-bearing mice treated with hematoporphyrin derivative (HpD). The aim of the study was to define the potential of this technique in the diagnosis of tumors by taking advantage of the long fluorescence lifetime of the exogenous dye with respect to the decay times of the natural fluorescence. After the administration of three different drug doses (5, 10 and 25 mg/kg body weight), fluorescence images were acquired at various uptake times (from 2 h to 10 d), to determine the best instrumental conditions and experimental procedure for the detection of tumors in the murine model considered. The optimal fluorescence contrast between the tumor area and the surrounding healthy tissue was found at 12 h after the administration of either 5 or 10 mg/kg HpD and was anticipated at 8 h for the highest drug dose. In this optimum condition, the tumor region could be identified even after the injection of 5 mg/kg HpD. A better fluorescence contrast was always obtained in 15 ns-delayed images with respect to synchronous ones.     

Two-step laser activation of hematoporphyrin derivative

A new photoactivation mechanism of hematoporphyrin derivative is presented. This process, based on the sequential absorption of two photons, leads to the production of cytotoxic radicals of HpD. The cytocidal efficiency is demonstrated by in vitro experiments.     

Stemodane Diterpenes and Diterpenoids: Isolation,Structure Elucidation,Biogenesis, Biosynthesis,Biological Activity,Biotransformations, Metabolites and Derivatives Biological Activity,Rearrangements

The scientific activity carried out over forty-five years on stemodane diterpenes and diterpenoids structure elucidation, biogenesis, biosynthesis, biological activity and biotransformations was reviewed.