Electrical properties of poly-trans-2,5-dimethylpiperazine-fumaramide. I.D.c. Conductivity by a new instrumentation

The d.c. conductivity of a recently synthesized polyamide, poly-trans-2,5-dimethylpiperazine-fumaramide, was investigated by a new instrumentation designed for measuring very low conductivity in insulating materials over broad ranges of temperature and environmental conditions. The instrumentation system allows measurements based on the voltmeter-ammeter method according to ASTM D-257, under atmospheres from high vacuum to a pressure of several times atmospheric of the desired gas and at temepratures from room to about 300°C, with an overall accuracy usually better than 10%. The material was examined in form of powder as well as film, in the dry and hydrated state, usually under vacuum up to about 200°C. The polymer behaves as an insulating material and exhibits a great increase in conductivity with water content. The results obtained do not permit a detailed discussion of the actual conduction mechanism. Although it seems to be primarily electronic in nature, an ionic contribution increasing with temperature cannot be excluded. There is no protonic contribution to the conduction because of the absence of N-H groups in the molecular chains.     

On the jumping conics of a semistable rank two vector bundle on P2

Stromme (see [S], (1.7)) introduced the notion of jumping conic of a normalized semistable rank two vector bundle E on ℙ² and he remarked that the locus of jumping conics of E has codimension ≤3+2c₁(E), with equality for general E. Here we introduce a concept of jumping conic of a semistable rank two vector bundle on ℙ² (see (I.1)) by generalizing the notion of jumping line of the second kind introduced by Hulek in [H]. Our definition agrees with Stromme's for c₁=−1, but not for c₁=0. In contrast with the case of jumping lines, where we have a different behaviour in the case c₁ even or c₁ odd, the set of jumping conics according to our definition is always a divisor (possibly empty) in the ℙ⁵ of all conics of ℙ² (see th. (I.8)), whose degree depends on c₂(E).     

The International Atomic Time and the Velocity of Light

Atomic clocks distributed around the world communicate with one another by means of radio signals. The synchronization signals sent by a transmitting station always reach the receiving station on time, at any hour of the day and in any season, despite the motion of the Earth. For some authors this means that these signals propagate isotropically (with one way velocity c), even with respect to the Earth's surface. In fact this may not be so; we show that the proper working of the network says nothing about the one-way velocity, as it is consistent with another theory, empirically (almost) equivalent to special relativity, in which the one-way speed of light has a directional dependence in moving frames.     

Rheological characterization of highly branched poly(ethyleneterephthalate)

Linear and highly branched poly(ethyleneterephthalate) samples were synthesized and characterized in terms of intrinsic viscosity, molecular weight and melt viscosity over a wide range of shear rates at several temperatures, in the range from 265° to 295 °C. Linear samples exhibited Newtonian behavior over a wide range of shear rates, while the branched ones became shear thinning at relatively low shear rates. Our experimental data, as well as data previously reported, were found to be described by a proposed correlation between the melt viscosity ratio and a branching index. Moreover, the activation energy for melt flow was found for the highly branched samples to be a little higher than that of the linear samples.     

Development of chemiluminescent assays for the quantitative detection and imaging of 5-bromo-2′deoxyuridine-labeled DNA in parvovirus B19-infected cells

Incorporation of exogenous analogues is a widely used method to evaluate DNA synthesis in cultured cells exposed to exogenous factors such as infectious agents. Herein, two new quantitative methodologies exploiting ultrasensitive chemiluminescence (CL) detection of 5-bromo-2′-deoxyuridine (BrdU) have been developed: a CL microscope imaging assay to evaluate BrdU labelling at single-cell level and a CL dot-blot assay to measure the amounts of DNA produced in the course of an in vitro infection of proliferating cells. The assays have been optimized on UT7/EpoS1 cells cultured in presence of different concentrations of BrdU (from 3 to 100 μM) and used to monitor parvovirus B19 (B19) life cycle in infected cells. The CL microscope imaging assay provided a detailed localization of BrdU-labelled nuclei allowing to count positive cells and measure their related CL intensity signals. The CL dot-blot assay, coupled with a B19 capture procedure performed with a specific peptide nucleic acid probe, has been designed to discriminate and selectively quantify cellular and viral BrdU-labelled genomes. Quantitative evaluation of BrdU-labelled B19 DNA has been achieved by means of a CL calibration curve. The high detectability, down to 2?×?10⁶ B19 genome copies, and the linear range extending up to 5?×?10⁸ copies make the method suitable to evaluate the amounts of B19 DNA produced throughout a replicative viral cycle.

Electronic sorting and recovery of single live cells from microlitre sized samples

Sorting and recovering specific live cells from samples containing less than a few thousand cells have become major hurdles in rare cell exploration such as stem cell research, cell therapy and cell based diagnostics. We describe here a new technology based on a microelectronic chip integrating an array of over 100,000 independent electrodes and sensors which allow individual and parallel single cell manipulation of up to 10,000 cells while maintaining viability and proliferation capabilities. Manipulation is carried out using dynamic dielectrophoretic traps controlled by an electronic interface. We also demonstrate the capabilities of the chip by sorting and recovering individual live fluorescent cells from an unlabeled population.